Journal of Clinical Lipidology (2014) 8, 287–295
Case Study
Genotype-phenotype relationships in patients with type I hyperlipoproteinemia Neema Chokshi, MD, Sarah D. Blumenschein, MD, Zahid Ahmad, MD, Abhimanyu Garg, MD* Division of Nutrition and Metabolic Diseases, Department of Internal Medicine, Center for Human Nutrition (Dr. Chokshi, Dr. Ahmad, and Dr. Garg), and Department of Pediatrics (Dr. Blumenschein), University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390 KEYWORDS: Type 1 hyperlipoproteinemia; Familial chylomicronemia syndrome; Lipoprotein lipase; GPIHBP1; Apolipoprotein A5
CONTEXT: Type I hyperlipoproteinemia (T1HLP) is a rare, autosomal recessive disorder characterized by extreme hypertriglyceridemia that fails to respond to lipid-lowering agents, predisposing to frequent attacks of acute pancreatitis. Mutations in lipoprotein lipase (LPL), apolipoprotein CII (APOC2), lipase maturation factor 1 (LMF1), glycosyl-phosphatidylinositol anchored high-density lipoprotein-binding protein 1 (GPIHBP1), and apolipoprotein AV (APOA5) cause T1HLP, but we lack data on phenotypic variations among the different genetic subtypes. OBJECTIVE: To study genotype-phenotype relationships among subtypes of T1HLP patients. DESIGN/INTERVENTION: Genetic screening for mutations in LPL, APOC2, GPIHBP1, LMF1, and APOA5. SETTING: Tertiary referral center. PATIENTS: Ten patients (7 female, 3 male) with chylomicronemia, serum triglyceride levels about 2000 mg/dL, and no secondary causes of hypertriglyceridemia. MAIN OUTCOME MEASURES: Genotyping and phenotypic features. RESULTS: Four patients harbored homozygous or compound heterozygous mutations in LPL, 3 had homozygous mutations in GPIHBP1, and 1 had a heterozygous APOA5 mutation. We failed to fully identify the genetic etiology in 2 cases: 1 had a heterozygous LPL mutation only and another did not have any mutations. We identified 2 interesting phenotypic features: the patient with heterozygous APOA5 mutation normalized triglyceride levels with weight loss and fish oil therapy, and all 7 female patients were anemic. CONCLUSIONS: Our data suggest the possibility of novel loci for T1HLP. We observed that heterozygous APOA5 mutation can cause T1HLP but such patients may unexpectedly respond to therapy, and females with T1HLP suffer from anemia. Further studies of larger cohorts may elucidate more phenotype-genotypes relationships among T1HLP subtypes. Published by Elsevier Inc. on behalf of National Lipid Association.
* Corresponding author. E-mail address: [email protected] Submitted October 2, 2013; revised January 7, 2014. Accepted for publication February 12, 2014.
Type I hyperlipoproteinemia (T1HLP, OMIM# 238600, also called familial chylomicronemia syndrome) is a rare, autosomal recessive disorder characterized by severe elevations in circulating triglycerides (TG) resulting from
1933-2874/$ - see front matter Published by Elsevier Inc. on behalf of National Lipid Association. http://dx.doi.org/10.1016/j.jacl.2014.02.006
288 accumulation of TG-rich lipoproteins, especially chylomicrons. Patients present with several physical findings: eruptive or tuberous xanthomas, lipemia retinalis, and hepatosplenomegaly. More concerning, severe hypertriglyceridemia predisposes to acute pancreatitis,1,2 a serious condition often complicated by the systemic inflammatory response syndrome, multiorgan failure, pancreatic necrosis, and mortality rates as high as 20%.3,4 T1HLP results from defects in the breakdown of chylomicrons, primarily due to deficiency of lipoprotein lipase (LPL). LPL binds to heparan sulfate, located at the heparin-binding site on the surface of capillary endothelial cells, allowing LPL to extend into the plasma and participate in the hydrolysis of TG carried in chylomicrons and very-low-density lipoproteins.5 More than 220 diseasecausing LPL mutations have been reported in more than 500 patients. Besides LPL, several additional loci have been identified for T1HLP, all of which encode for either cofactors or proteins involved in LPL’s maturation or binding to endothelium: apolipoprotein CII (APOC2),6 lipase maturation factor 1 (LMF1),7 glycosyl-phosphatidylinositol anchored high-density lipoprotein-binding protein 1 (GPIHBP1),8,9 and apolipoprotein AV (APOA5).10–13 APOC2 is synthesized in the liver and subsequently secreted into the plasma. APOC2 is found on high-density lipoproteins (HDL), chylomicrons, and very-low-density lipoproteins, and acts as an activator for LPL. LMF1 serves as a chaperone of the endoplasmic reticulum and is required for the posttranslational activation of LPL by dimerizing inactive monomers of LPL into active enzymes.14 GPIHBP1 is a capillary endothelial protein that transports LPL into capillaries15 and provides a platform for LPL-mediated hydrolysis of chylomicrons.16 APOA5 plays a role in reducing triglycerides, most likely by stimulating LPL.17 Mutations in other loci besides LPL are found infrequently in patients with T1HLP. Our review of the literature reveals only 20 families with disease-causing mutations in APOC218–33; 12 families with GPIHBP1 mmtations15,16,34; 2 patients with LMF1 mmtations7,35; and 5 patients with homozygous mutations in APOA5.10–13 We lack data on whether subtle phenotypic variations exist in patients with the various genetic subtypes of T1HLP. Therefore, we carefully evaluated our patients with T1HLP and ascertained their genotype-phenotype relationships.
Materials and methods All patients or their legal guardians gave written informed consent, and the Institutional Review Board of the University of Texas Southwestern Medical Center approved the protocol. T1HLP patients were ascertained from specialty lipid clinics in the Dallas, TX, area. Inclusion criteria consisted of a history of chylomicronemia with serum TG levels above 2000 mg/dL. We excluded patients with hypertriglyceridemia resulting from a secondary
Journal of Clinical Lipidology, Vol 8, No 3, June 2014 cause such as diabetes mellitus (if it was diagnosed before onset of hypertriglyceridemia and pancreatitis), alcoholism, renal insufficiency, untreated hypothyroidism, or the use of estrogen or other medications. Detailed personal and family history regarding hypertriglyceridemia, pancreatitis, medication use, and xanthomas was obtained. Patients were examined for the presence of lipemia retinalis and eruptive or tuberous xanthomas.
Candidate gene analysis Genomic DNA was isolated from whole blood using the Easy-DNA kit (Invitrogen, Carlsbad, CA). All exons and the flanking intronic regions of LPL, APOC2, GPIHBP1, LMF1, and APOA5 were amplified and sequenced using Applied Biosystems’ 3730xl DNA Analyzer (Applied Biosystems, Carlsbad, CA). The genes were sequenced sequentially: LPL, APOC2, GPIHBP1, LMF1, and then APOA5.
Lipids and lipoproteins Medical charts were reviewed to obtain historic lipid levels. All centers measured fasting total cholesterol, TG, and HDL-cholesterol (HDL-C) using enzymatic assays in commercial laboratories.
Results Ten patients with T1HLP were evaluated (Fig. 1, Table 1). Of these, 7 were female and 3 were male. The mean age of our patients was 32.6 years (range, 5 to 45 years). The age at time of diagnosis varied from infancy to the early 30s with a mean age of 12.5 years; however, most patients had some symptoms in childhood. Only 1 patient had a history of parental consanguinity. A history of acute pancreatitis was a common finding among our patients. Although 1 patient with a confirmed mutation in LPL had no history of pancreatitis, he had chronic, recurring abdominal pain since childhood. Three of our patients have had 1 episode of acute pancreatitis, and the remaining 6 have had multiple episodes (up to 15) of pancreatitis. The mean body mass index (BMI) was 26.1 kg/m2. Four patients had hepatosplenomegaly. The mean total cholesterol level was 310 mg/dL, fasting serum triglyceride level was 3252 mg/dL, and HDL-C level was 21 mg/dL (Table 2). All patients had a history of fasting serum TG levels above 2000 mg/dL. The mean hemoglobin concentration was 11.2 g/dL, and all 7 female patients were anemic. Genetic testing revealed 4 patients with disease-causing variants in LPL (3 with homozygous mutations and 1 with compound heterozygous mutations), 1 patient with a heterozygous LPL mutation, 3 patients with homozygous GPIHBP1 mutations, 1 patient with a heterozygous APOA5 mutation, and 1 patient without any diseasecausing mutations.
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Figure 1 Pedigrees of our patients with type 1 hyperlipoproteinemia. Squares, males; circles, females; filled symbols, affected subjects; open symbols, unaffected subjects; diagonal line, deceased subject; arrow, proband; double horizontal line, consanguineous marriage.
Case reports Case 1 (T1HLP 1.7) This 36-year-old Asian Indian female was first diagnosed with a lipid disorder at the age of 1 year. During childhood, she recalled multiple episodes of abdominal pain and experienced around 2 episodes of acute pancreatitis per year from the ages of 6 to 16 years. Subsequently, for a 10-year period, she experienced no episodes of acute pancreatitis. At age 26 years, during her first pregnancy, she again developed acute pancreatitis requiring hospitalization. Since that time, she has had at least 5 hospitalizations for acute pancreatitis. There was no known consanguinity among the parents. She had no history of diabetes, estrogen use, or alcohol use. Her brother was known to have elevated serum triglycerides, but not exceeding 1000 mg/dL. On examination, she had lipemia retinalis and hepatosplenomegaly with the liver palpable 4 cm below the right costal margin. She had no xanthomas. The highest fasting serum triglyceride level at our institution was 2476 mg/dL; however, she recalls serum triglyceride levels of 9000 to 10,000 mg/dL in the past. She was
also anemic with a hemoglobin concentration of 9.7 g/dL and a mean corpuscular volume (MCV) of 81 fL. Her liver function tests were normal. The patient was found to have a homozygous mutation in LPL (c.IVS211G.A). She was asked to follow an extremely low-fat diet, and her triglyceride levels decreased; however, they remain higher than 1000 mg/dL.
Case 2 (T1HLP 2.4) This 21-year-old Asian Indian female was first noted to have high triglycerides at 1 month of age. She had been hospitalized for acute pancreatitis 3 times; however, she had bouts of abdominal pain since childhood, which occurred about once a month with the ingestion of a high-fat meal. She did not follow any particular diet, but had learned to avoid fatty foods. She had no history of estrogen or alcohol use, and no history of diabetes. There was no known consanguinity among her parents. Her medications at the initial visit included fenofibrate 134 mg/day and fish oil 1 capsule daily. She was a thin young female with pale conjunctiva, lipemia retinalis, and mild hepatosplenomegaly. She had no eruptive xanthomas.
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Table 1
Demographic and clinical features of patients with type 1 hyperlipoproteinemia Mutation
Case #
Age/ethnicity/sex
Age of onset
BMI (kg/m2)
gene
Het/Hom
Nucleotide
Protein
1 2
36/Indian/F 21/Indian/F
1 year 1 month
28.1 19.2
LPL LPL
3 4
42/Indian/M 44/Hispanic/F
29 years 25 years
20.2 31.6
LPL LPL
hom het het hom hom
IVS211G.A 721C.T IVS112insT IVS1-1G.C 1051G.A
— P241S — — G351R
5 6 7 8 9
40/El Salvadorian/F 5/Indian/M 29/Mexican/F 45/Caucasian/F 45/Colombian/F
24 years 2 months 23 years 10 years 13 years
25.8 * 28.4 26.4 35.6
GPIHBP1 GPIHBP1 APOA5 LPL —
hom hom het het
203G.A del 289C.T 644G.A —
C68Y del Q97X G215E —
10
19/Indian/M
2 months
19.8
GPIHBP1
hom
del
del
Pancreatitis, # of episodes
HSM
Anemia
Lipid-lowering drugs tried
Response to fibrates/fish oil
15 3
Yes Yes
Yes Yes
Fish oil, gemfibrozil Fenofibrate, fish oil
No No
0 1
No No
No Yes
No No
.10 1 2 2 7
Yes No No No Yes
Yes No Yes Yes Yes
1
No
No
Fish oil Fenofibrate, fish oil, niacin, simvastatin Fish oil, gemfibrozil None Fish oil Fenofibrate, fish oil Fenofibrate, fish oil, rosuvastatin None
No Yes No No -
BMI, body mass index; Het, heterozygous; Hom, homozygous; HSM, hepatosplenomegaly. *3rd percentile for weight.
Laboratory values for patients with type 1 hyperlipoproteinemia
Case #
Total cholesterol (mg/dL)
Triglycerides (mg/dL)
HDL-C (mg/dL)
Hgb (g/dL)
Hct (%)
MCV (fL)
Iron (mg/dL)
1 2 3 4 5 6 7 8 9 10
197 255 344 269 600 177 235 441 462 121
2476 3090 4840 1522 1960 1578 2000 4120 5790 1140
17 23 41 16 18 11 26 37 12 13
9.7 8.9 13.2 10.9 8.8 12.7 11.2 8.6 10.6 17.2
30.3 28.7 39.5 31.3 28.0 35.7 33.7 29.8 29.1 48.3
81 83.4 83.9 85.8 73.7 81.3 75.2 82.1 85.6 86.9
58 69 102 42 39 81 20 39 47 117
TIBC (mg/dL)
Ferritin (ng/mL)
69*
86*
398 509
30 20
335
81
AST (U/L)
ALT (U/L)
Menses
20 23 58 20 21 29 84 31 16 24
10 12 34 17 13 14 85 34 12 24
N H Male H H Male N H ## Male
##, hysterectomy age 27 years; ALT, alanine aminotransferase; AST, aspartate aminotransferase; H, heavy flow; Hct, hematocrit; HDL-C, high-density lipoprotein cholesterol; Hgb, hemoglobin; MCV, mean corpuscular volume; N, normal flow; TIBC, total iron-binding capacity. Normal ranges: Hemoglobin male 13.2–17.1 g/dL, hemoglobin female 11.7–15.5 g/dL; hematocrit male 38.5–50%, hematocrit female 35–45%; MCV 80–100 fL; iron male 45–170 mg/dL, iron female 40– 175 mg/dL; AST 10–30 U/L; ALT 6–40 U/L; TIBC 149–491 mg/dL (*271–448 mg/dL); ferritin 13–150 ng/mL (*10–143 ng/mL).
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Table 2
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The highest serum triglyceride level at our institution was .4425 mg/dL; however, her father recalled a triglyceride level around 19,000 mg/dL in the past. She was also noted to have a chronic normocytic anemia, with a hemoglobin concentration of 8.9 g/dL and MCV of 83.4 fL. She had compound heterozygous mutations in LPL (c.721C.T [p.P241S] and c.IVS112insT). Because fish oil and fenofibrate did not result in a reduction of triglyceride levels, they were discontinued. She was started on orlistat 120 mg orally 3 times a day in an attempt to reduce fat absorption from the diet. The patient believes that her attacks of abdominal pain have decreased in frequency since starting orlistat. Her serum triglycerides have ranged from 667 to 1803 mg/dL. She has some oily stools with the medication, but is able to tolerate it.
Case 3 (T1HLP 3.12) This 42-year-old Asian Indian male was first noted to have high triglycerides at around age 29 years during a routine blood test. On direct questioning, he recalled many episodes of abdominal pain as a child, but denied hospitalizations for acute pancreatitis and could not recall having eruptive xanthomas. He drank alcohol only occasionally (1 to 2 beers on weekends). He had a history of hypothyroidism that was adequately treated with levothyroxine. There was no history of consanguinity between his parents, and he had no history of diabetes. He was a thin male with lipemia retinalis on funduscopic examination, but he had no hepatosplenomegaly or xanthomas. His serum triglyceride levels had been as high as 4840 mg/dL. He had a homozygous LPL mutation (c.IVS1-1G.C). He was placed on omega-3-acid ethyl esters 2 capsules twice a day and asked to follow a very low-fat diet. His serum triglycerides remain about 2000 mg/dL.
Case 4 (T1HLP 4.12) This 44-year-old Hispanic female was first noted to have high triglycerides during pregnancy at age 25 years. She had had 1 episode of pancreatitis that required hospitalization at age 38 years. She denied a history of estrogen use. She denied alcohol use but was consuming a white winegarlic drink. She had hypothyroidism, adequately treated with levothyroxine, and no history of diabetes. Her father and mother were first cousins. She had been taking fenofibrate 200 mg daily, fish oil 3 capsules daily, simvastatin 40 mg daily, and niacin 500 mg daily for more than 10 years. She had a BMI of 31.6 kg/m2 and also had lipemia retinalis. She had no acanthosis nigricans, hepatosplenomegaly, or xanthomas. Her triglycerides were elevated up to 3675 mg/dL despite compliance with her medications. She was found to have a normocytic anemia with a hemoglobin concentration of 10.9 g/dL. She had a homozygous mutation in LPL (c.1051G.A [p.G351R]). She was asked to follow an extremely low-fat diet and discontinue the
291 white wine-garlic drink. Her serum triglycerides improved, but remain just above 1000 mg/dL.
Case 5 (T1HLP 5.9) This previously reported 40-year-old El Salvadorian female was first diagnosed with hypertriglyceridemia during pregnancy at age 24 years.34 She had experienced intermittent abdominal pain since childhood, and had numerous hospitalizations resulting from acute pancreatitis. She noted that her abdominal pain improved by avoidance of fat in her diet. She denied the use of estrogen. She had no history of diabetes and no history of consanguinity among the parents. One of her brothers had T1HLP and a history of acute pancreatitis. She had been taking gemfibrozil 600 mg twice a day and fish oil 1 g 3 times a day for 1 year. Her BMI was 25.8 kg/m2. She had hepatosplenomegaly and was noted to have eruptive xanthomas on her elbows. There was no lipemia retinalis. The maximum triglyceride levels were 9600 mg/dL. She was anemic with a hemoglobin concentration of 8.8 g/dL and MCV of 73.7 fL. She had a homozygous mutation in GPIHBP1 (c.203G.A [p.C68Y]). She was asked to follow a low-fat diet and her TG level improved; however, it remains higher than 1000 mg/dL.
Case 6 (T1HLP 6.31) This previously reported 5-year-old Asian Indian boy initially presented at 2 months of age.34 At that time, he presented with lethargy and anemia, and was noted to have ‘‘strawberry-pink’’ blood. His serum triglyceride level was found to be .20,000 mg/dL. His hospital course was complicated by shock and severe anemia requiring intensive care. His mother recalled that he had pancreatitis while in the intensive care unit, but there was no clear mention of it in the hospital records. He had no further episodes of pancreatitis. He occasionally had reddish bumps on his buttocks, and occasionally had postprandial abdominal pain. He followed a low-fat diet. Both parents were from Gujarat, India; however, there was no known history of consanguinity. The patient had a distant aunt on his mother’s side and a distant cousin on his father’s side (case 10) who also had T1HLP. He was at the 25th percentile for height and 3rd percentile for weight. He had lipemia retinalis on funduscopic examination and a grade II/VI systolic murmur loudest at the apex. He had no hepatosplenomegaly or eruptive xanthomas. He had a homozygous mutation causing a deletion of the entire GPIHBP1 gene.34 His triglycerides remain elevated at 2000 mg/dL.
Case 7 (T1HLP 7.8) This 29-year-old Mexican female was first diagnosed with hypertriglyceridemia at age 23 years. She recalled intermittent abdominal pain with nausea and vomiting in
292 her teenage years. She also recalled yellow-red bumps that appeared on her back and flexor surface of her knees during those years but never required hospitalization in childhood. At ages 24 and 26, though, she was hospitalized for acute pancreatitis resulting from hypertriglyceridemia. She reported abdominal pain following ingestion of fatty foods. She had no history of diabetes or estrogen or steroid use. She did not drink alcohol, and there was no parental consanguinity. Her maternal grandmother had a history of pancreatitis, but it is unknown if she had high triglycerides. Her BMI was 28.4 kg/m2. She had hepatomegaly, but no acanthosis nigricans or xanthomas. Her serum triglycerides were elevated to 2000 mg/dL. Genetic testing found no mutation in LPL, APOC2, GPIHBP1, or LMF1. However, she had a heterozygous mutation in APOA5 (c.289C.T [p.Q97X]). She was started on fish oil 12 capsules daily. She lost 6 kg of weight, and eventually her triglyceride levels decreased to 71 mg/dL.
Case 8 (T1HLP 8.3) This 45-year-old white female was first noted to have high triglycerides at age 10 or 11 years. She recalled taking gemfibrozil as a teenager and noted that her blood was ‘‘white’’ and ‘‘milky.’’ She had had 2 episodes of acute pancreatitis in the past; the first episode was during her first pregnancy at age 28 years and the second at age 36 years. She did not recall chronic abdominal pain or skin rashes. She took an oral contraceptive pill briefly when she was first married, but not otherwise. She did not drink alcohol and did not have diabetes. She was taking fenofibric acid 135 mg daily. She was also prescribed fish oil 2 capsules twice a day, but was not taking this consistently. Her BMI was 26.4 kg/m2. Lipemia retinalis was noted on funduscopy. There was no acanthosis nigricans, organomegaly, or eruptive xanthomas. Her fasting serum triglyceride level was 4120 mg/dL, HbA1c was 5.4%, and she had a normocytic anemia with a hemoglobin concentration of 8.6 g/dL and MCV of 82.1 fl. She had a heterozygous mutation in LPL (c.644G.A [p.G215E]). No mutations were found in APOC2, GPIHBP1, LMF1, and APOA5.
Case 9 (T1HLP 9.8) This 45-year-old Colombian female was first diagnosed with hypertriglyceridemia at age 13 years. She had the first episode of pancreatitis at age 21 years during her first pregnancy and subsequently had 6 more episodes. She developed diabetes at age 39 years, which was controlled with insulin. She had a history of coronary artery disease (CAD) with stent placement at age 42 years. She took oral contraceptive pills on and off in her 20s. She did not drink alcohol, and there was no history of consanguinity among the parents. Her BMI was 35.6 kg/m2. She did not have xanthomas or lipemia retinalis, but had mild hepatomegaly and splenomegaly. Her triglyceride level was 5790 mg/dL
Journal of Clinical Lipidology, Vol 8, No 3, June 2014 and HbA1c was 7%. She was anemic with a hemoglobin concentration of 10.6 g/dL and MCV of 85.6 fL. Genotyping for LPL, APOC2, GPIHBP1, LMF1, and APOA5 revealed no disease-causing variants.
Case 10 (T1HLP 6.29) This 19-year-old Asian Indian male was first noted to have high triglycerides as an infant. At age 2 months, he presented with a fever and was found to have a triglyceride level of w25,000 mg/dL. He had an episode of pancreatitis at age 2. Since then, he has had bouts of abdominal pain, especially after eating seafood and high-fat foods. The abdominal pain was occasionally associated with nausea, vomiting, and diarrhea. When he followed an extremely low-fat diet, he noted fewer episodes of abdominal pain. He had no other medical conditions and no history of diabetes or alcohol use. He took no medications. His parents were distantly related, and the patient had a distant cousin with T1HLP (case 6). He was thin with a BMI of 19.8 kg/m2. There was no lipemia retinalis on funduscopic examination. He had no hepatosplenomegaly or xanthomas. His triglyceride level was 1140 mg/dL. He was not anemic, and his liver function tests were normal. Genetic testing revealed the same large, homozygous deletion of GPIHBP1 as reported previously.34
Discussion Our case series suggests that LPL deficiency is the most prevalent cause of T1HLP, followed by other extremely rare subtypes with GPIHBP1 deficiency and APOA5 mutation. No patient had a mutation in APOC2 or LMF1. Furthermore, in 2 patients, we were unable to fully explain the phenotype based on the results of genetic testing, suggesting further genetic heterogeneity and the possibility of novel loci for T1HLP. Case 9 developed hypertriglyceridemia during childhood, and although she developed diabetes, it was not until after she suffered from multiple episodes of acute pancreatitis. Although we cannot exclude the remote possibility of a small deletion or promoter/intronic mutation in the known T1HLP genes, her case suggests the possibility of an undiscovered T1HLP locus. Case 8 harbored only a heterozygous mutation in LPL. Heterozygous LPL mutations result in decreased LPL activity and mass, mild combined hyperlipidemia, and reduced HDL-C.36 Only in the presence of secondary factors (eg, uncontrolled diabetes, heavy alcohol intake, estrogen therapy), do subjects with heterozygous LPL mutations develop type 5 hyperlipoproteinemia. However, the clinical presentation in case 8 resembles the other T1HLP cases more so than type 5 hyperlipoproteinemia—specifically, she lacked any secondary factors. Thus, either we failed to identify a second LPL mutation on Sanger sequencing or she harbors a mutation in an undiscovered T1HLP locus.
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T1HLP occurs with homozygous APOA5 mutations, but case 7 harbored only a heterozygous APOA5 mutation. Patients with heterozygous APOA5 mutations have previously been reported to display variable serum triglyceride levels, ranging from mild to extremely high levels without a secondary cause.10–13 Our patient clinically presented with T1HLP; however, her TG levels improved with fish oil and weight loss. This is in contrast to all the other patients with LPL or GPIHBP1 deficiency who continued to have extremely high TG concentrations despite fibrates and/or fish oil therapy. LPL deficiency should result in a lack of TG storage in adipose tissue—a ‘‘lipodystrophic’’ phenotype. Yet, most of our patients were overweight (BMI range 19.2–35.6 kg/m2) with a normal fat distribution; BMI did not differ by T1HLP etiology. These findings suggest alternative adipocyte-specific lipases that may be upregulated in the absence of LPL or its cofactors. Anemia has been previously reported in a case series of infants presenting with T1HLP37; 7 of 16 infants presented with a normocytic anemia resulting from an unknown cause, and both male and female infants were affected. Reports of T1HLP adults with anemia are scarce. In our female patients, hemoglobin concentration ranged from 8.6 to 10.9 g/dL (Table 2). The serum iron level was also found to be low in nearly all females. The anemia in these patients was chronic, and the hemoglobin concentrations did not seem to correlate with serum TG levels. The red blood cell MCV was low to low-normal in these patients, suggesting iron deficiency or anemia of chronic disease. The possibility of artifactual reduction of hematocrit resulting from severe chylomicronemia was considered, but it is less likely because our male patients lacked anemia despite similar hypertriglyceridemia. Of our female patients, 4 had menorrhagia, 2 had normal menstrual periods, and 1 had a hysterectomy. Serum ferritin and total ironbinding capacity were measured in 3 patients with menorrhagia and 2 of them were confirmed to have iron deficiency anemia. The etiology of the anemia remains unclear. Possible explanations include bone marrow suppression, splenic sequestration, menorrhagia, or spurious values in the setting of chylomicronemia. The relationship between chylomicronemia and premature cardiovascular disease remains controversial. Only 1 patient suffered from CAD (case 9), and she had developed diabetes before the diagnosis of CAD. Although most cases of T1HLP in the literature are not associated with the development of CAD, there have been case reports of patients with LPL mutations who developed premature atherosclerosis.38,39 Two patients with GPIHBP1 mutations and CAD have been reported as well.8,40 No clear mechanism for the development of atherosclerosis in these patients has been elucidated from the reports. The management of T1HLP is challenging for absence of any clinical trials of lipid-lowering drugs. Our
293 experience and previous anecdotal reports suggest that the current TG lowering agents—niacin, fibrates, and fish oil— are ineffective, and despite these therapies, patients continue to have episodes of abdominal pain and acute pancreatitis. The only option is to drastically reduce their fat intake to 10% to 15% of total energy to minimize chylomicron formation. This extremely low-fat diet may reduce serum TG levels to less than 2000 mg/dL (as in cases 1, 3, 4, 5, and 10), greatly mitigating the risk of acute pancreatitis, although the durability and feasibility of this extreme diet remains unknown. Heparin has been investigated as a therapeutic option for T1HLP patients with GPIHBP1 mutations, but reports are conflicting. Heparin administration reduced TG levels in GPIHBP1-deficient mice,41 and in 1 young boy, a 6-hour heparin infusion markedly reduced TG levels.42 Additional human studies, however, failed to show a reduction in plasma TG upon heparin administration to GPIHBP1deficient patients.34,42,43 Thus, unfortunately, low-dose heparin therapy may not be of therapeutic benefit to those with GPIHBP1 deficiency. The European Commission recently approved an LPL gene therapy called alipogene tiparvovec, which is composed of the LPL gene along with an adeno-associated virus subtype 1 (AAV1) vector (AAV1-LPLS447x).44 A study of alipogene tiparvovec in patients with LPL deficiency showed an initial reduction in serum TG by 40%, although TG returned to baseline by month 6 despite clear long-term transgene expression.44 Still, patients reported improvement in quality of life and an overall reduction of the incidence of acute pancreatitis and/or intensity of the crisis. However, alipogene tiparvovec may not be useful for T1HLP patients with mutations in APOC2, APOA5, LMF1, and GPIHBP1. Other potential therapeutic options in T1HLP patients are under investigation, such as an intestinal lipase inhibitor, orlistat; a diacylglycerol acyltransferase inhibitor, LCQ908; an intestinal-specific microsomal triglyceride transfer protein 1 inhibitor, SLx-4090; and an APOC3 inhibitor. In summary, our data suggest further genetic heterogeneity in T1HLP with the possibility of novel loci. Furthermore, understanding of phenotypic differences among various subtypes of T1HLP will require careful phenotyping of larger cohorts of patients belonging to each subtype.
Acknowledgments We thank Sarah Masood and Tommy Hyatt for technical assistance and Claudia Quittner for study coordination. The study was supported by the Southwest Medical Foundation. Disclosure Statement: A.G. is a consultant and on the advisory board for Pfizer and Bristol-Myers-Squibb, speaker for Merck, and a consultant for Aegerion. Z.A. is on the speaker’s bureau for Sanofi-Aventis and attended an advisory board for Aegerion Pharmaceuticals. N.C. and S.B. have nothing to disclose.
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References 1. Brunzell JD. Clinical practice. Hypertriglyceridemia. N Engl J Med. 2007;357:1009–1017. 2. Fortson MR, Freedman SN, Webster PD 3rd. Clinical assessment of hyperlipidemic pancreatitis. Am J Gastroenterol. 1995;90:2134–2139. 3. Banks PA, Freeman ML. Practice guidelines in acute pancreatitis. Am J Gastroenterol. 2006;101:2379–2400. 4. Gloor B, Muller CA, Worni M, Martignoni ME, Uhl W, Buchler MW. Late mortality in patients with severe acute pancreatitis. Br J Surg. 2001;88:975–979. 5. Cheng CF, Oosta GM, Bensadoun A, Rosenberg RD. Binding of lipoprotein lipase to endothelial cells in culture. J Biol Chem. 1981;256: 12893–12898. 6. Brunzell JD, Deeb SS. Familial lipoprotein lipase deficiency, Apo C-II deficiency, and hepatic lipase deficiency. In: Scriver CR, Beaudet BL, Sly WS, Valle D, editors. The Metabolic and Molecular Bases of Inherited Disease. New York: The McGraw-Hill Companies, 2006. 7. Peterfy M, Ben-Zeev O, Mao HZ, et al. Mutations in LMF1 cause combined lipase deficiency and severe hypertriglyceridemia. Nat Genet. 2007;39:1483–1487. 8. Wang J, Hegele RA. Homozygous missense mutation (G56R) in glycosylphosphatidylinositol-anchored high-density lipoproteinbinding protein 1 (GPI-HBP1) in two siblings with fasting chylomicronemia (MIM 144650). Lipids Health Dis. 2007;6:23. 9. Beigneux AP, Franssen R, Bensadoun A, et al. Chylomicronemia with a mutant GPIHBP1 (Q115P) that cannot bind lipoprotein lipase. Arterioscler Thromb Vasc Biol. 2009;29:956–962. 10. Priore Oliva C, Carubbi F, Schaap FG, Bertolini S, Calandra S. Hypertriglyceridaemia and low plasma HDL in a patient with apolipoprotein A-V deficiency due to a novel mutation in the APOA5 gene. J Intern Med. 2008;263:450–458. 11. Marcais C, Verges B, Charriere S, et al. Apoa5 Q139X truncation predisposes to late-onset hyperchylomicronemia due to lipoprotein lipase impairment. J Clin Invest. 2005;115:2862–2869. 12. Priore Oliva C, Pisciotta L, Li Volti G, et al. Inherited apolipoprotein A-V deficiency in severe hypertriglyceridemia. Arterioscler Thromb Vasc Biol. 2005;25:411–417. 13. Priore Oliva C, Tarugi P, Calandra S, et al. A novel sequence variant in APOA5 gene found in patients with severe hypertriglyceridemia. Atherosclerosis. 2006;188:215–217. 14. Peterfy M. Lipase maturation factor 1: a lipase chaperone involved in lipid metabolism. Biochim Biophys Acta. 2012;1821:790–794. 15. Davies BS, Beigneux AP, Barnes RH 2nd, et al. GPIHBP1 is responsible for the entry of lipoprotein lipase into capillaries. Cell Metab. 2010;12:42–52. 16. Beigneux AP, Davies BS, Gin P, et al. Glycosylphosphatidylinositolanchored high-density lipoprotein-binding protein 1 plays a critical role in the lipolytic processing of chylomicrons. Cell Metab. 2007;5: 279–291. 17. Nilsson SK, Heeren J, Olivecrona G, Merkel M. Apolipoprotein A-V: a potent triglyceride reducer. Atherosclerosis. 2011;219:15–21. 18. Baggio G, Manzato E, Gabelli C, et al. Apolipoprotein C-II deficiency syndrome. Clinical features, lipoprotein characterization, lipase activity, and correction of hypertriglyceridemia after apolipoprotein C-II administration in two affected patients. J Clin Invest. 1986;77: 520–527. 19. Beil FU, Fojo SS, Brewer HB Jr., Greten H, Beisiegel U. Apolipoprotein C-II deficiency syndrome due to apo C-IIHamburg: clinical and biochemical features and HphI restriction enzyme polymorphism. Eur J Clin Invest. 1992;22:88–95. 20. Breckenridge WC, Alaupovic P, Cox DW, Little JA. Apolipoprotein and lipoprotein concentrations in familial apolipoprotein C-II deficiency. Atherosclerosis. 1982;44:223–235.
Journal of Clinical Lipidology, Vol 8, No 3, June 2014 21. Breckenridge WC, Little JA, Steiner G, Chow A, Poapst M. Hypertriglyceridemia associated with deficiency of apolipoprotein C-II. N Engl J Med. 1978;298:1265–1273. 22. Cox DW, Breckenridge WC, Little JA. Inheritance of apolipoprotein C-II deficiency with hypertriglyceridemia and pancreatitis. N Engl J Med. 1978;299:1421–1424. 23. Fellin R, Baggio G, Poli A, et al. Familial lipoprotein lipase and apolipoprotein C-II deficiency. Lipoprotein and apoprotein analysis, adipose tissue and hepatic lipoprotein lipase levels in seven patients and their first degree relatives. Atherosclerosis. 1983;49: 55–68. 24. Fojo SS, Baggio G, Gabelli C, et al. Apolipoprotein C-II deficiency: identification of a structural variant ApoC-II Padova. Biochem Biophys Res Commun. 1988;154:73–79. 25. Fojo SS, de Gennes JL, Chapman J, et al. An initiation codon mutation in the apoC-II gene (apoC-II Paris) of a patient with a deficiency of apolipoprotein C-II. J Biol Chem. 1989;264: 20839–20842. 26. Fojo SS, Lohse P, Parrott C, et al. A nonsense mutation in the apolipoprotein C-IIPadova gene in a patient with apolipoprotein C-II deficiency. J Clin Invest. 1989;84:1215–1219. 27. Fojo SS, Stalenhoef AF, Marr K, Gregg RE, Ross RS, Brewer HB Jr. A deletion mutation in the ApoC-II gene (ApoC-II Nijmegen) of a patient with a deficiency of apolipoprotein C-II. J Biol Chem. 1988; 263:17913–17916. 28. Kawano M, Kodama K, Inadera H, et al. A case of apolipoprotein C-II deficiency with coronary artery disease. Clin Exp Med. 2002;2: 29–31. 29. Ohno M, Ishibashi S, Nakao K, et al. A neonatal case of apolipoprotein C-II deficiency. Eur J Pediatr. 1989;148:550–552. 30. Okubo M, Hasegawa Y, Aoyama Y, Murase T. A G11 to C mutation in a donor splice site of intron 2 in the apolipoprotein (apo) C-II gene in a patient with apo C-II deficiency. A possible interaction between apo C-II deficiency and apo E4 in a severely hypertriglyceridemic patient. Atherosclerosis. 1997;130:153–160. 31. Takase S, Osuga J, Fujita H, et al. Apolipoprotein C-II deficiency with no rare variant in the APOC2 gene. J Atheroscler Thromb. 2013;20: 481–493. 32. Wilson CJ, Priore Oliva C, Maggi F, Catapano AL, Calandra S. Apolipoprotein C-II deficiency presenting as a lipid encephalopathy in infancy. Ann Neurol. 2003;53:807–810. 33. Yamamura T, Sudo H, Ishikawa K, Yamamoto A. Familial type I hyperlipoproteinemia caused by apolipoprotein C-II deficiency. Atherosclerosis. 1979;34:53–65. 34. Rios JJ, Shastry S, Jasso J, et al. Deletion of GPIHBP1 causing severe chylomicronemia. J Inherit Metab Dis. 2012;35:531–540. 35. Cefalu AB, Noto D, Arpi ML, et al. Novel LMF1 nonsense mutation in a patient with severe hypertriglyceridemia. J Clin Endocrinol Metab. 2009;94:4584–4590. 36. Babirak SP, Iverius PH, Fujimoto WY, Brunzell JD. Detection and characterization of the heterozygote state for lipoprotein lipase deficiency. Arteriosclerosis. 1989;9:326–334. 37. Feoli-Fonseca JC, Levy E, Godard M, Lambert M. Familial lipoprotein lipase deficiency in infancy: clinical, biochemical, and molecular study. J Pediatr. 1998;133:417–423. 38. Benlian P, De Gennes JL, Foubert L, Zhang H, Gagne SE, Hayden M. Premature atherosclerosis in patients with familial chylomicronemia caused by mutations in the lipoprotein lipase gene. N Engl J Med. 1996;335:848–854. 39. Saika Y, Sakai N, Takahashi M, et al. Novel LPL mutation (L303F) found in a patient associated with coronary artery disease and severe systemic atherosclerosis. Eur J Clin Invest. 2003;33: 216–222. 40. Yamamoto H, Onishi M, Miyamoto N, et al. Novel combined GPIHBP1 mutations in a patient with hypertriglyceridemia associated with CAD. J Atheroscler Thromb. 2013;20:777–784.
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41. Weinstein MM, Yin L, Beigneux AP, et al. Abnormal patterns of lipoprotein lipase release into the plasma in GPIHBP1-deficient mice. J Biol Chem. 2008;283:34511–34518. 42. Franssen R, Young SG, Peelman F, et al. Chylomicronemia with low postheparin lipoprotein lipase levels in the setting of GPIHBP1 defects. Circ Cardiovasc Genet. 2010;3:169–178.
295 43. Olivecrona G, Ehrenborg E, Semb H, et al. Mutation of conserved cysteines in the Ly6 domain of GPIHBP1 in familial chylomicronemia. J Lipid Res. 2010;51:1535–1545. 44. Gaudet D, Methot J, Dery S, et al. Efficacy and long-term safety of alipogene tiparvovec (AAV1-LPL(S447X)) gene therapy for lipoprotein lipase deficiency: an open-label trial. Gene Ther. 2013;20:361–369.
Case Study
Genotype-phenotype relationships in patients with type I hyperlipoproteinemia Neema Chokshi, MD, Sarah D. Blumenschein, MD, Zahid Ahmad, MD, Abhimanyu Garg, MD* Division of Nutrition and Metabolic Diseases, Department of Internal Medicine, Center for Human Nutrition (Dr. Chokshi, Dr. Ahmad, and Dr. Garg), and Department of Pediatrics (Dr. Blumenschein), University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390 KEYWORDS: Type 1 hyperlipoproteinemia; Familial chylomicronemia syndrome; Lipoprotein lipase; GPIHBP1; Apolipoprotein A5
CONTEXT: Type I hyperlipoproteinemia (T1HLP) is a rare, autosomal recessive disorder characterized by extreme hypertriglyceridemia that fails to respond to lipid-lowering agents, predisposing to frequent attacks of acute pancreatitis. Mutations in lipoprotein lipase (LPL), apolipoprotein CII (APOC2), lipase maturation factor 1 (LMF1), glycosyl-phosphatidylinositol anchored high-density lipoprotein-binding protein 1 (GPIHBP1), and apolipoprotein AV (APOA5) cause T1HLP, but we lack data on phenotypic variations among the different genetic subtypes. OBJECTIVE: To study genotype-phenotype relationships among subtypes of T1HLP patients. DESIGN/INTERVENTION: Genetic screening for mutations in LPL, APOC2, GPIHBP1, LMF1, and APOA5. SETTING: Tertiary referral center. PATIENTS: Ten patients (7 female, 3 male) with chylomicronemia, serum triglyceride levels about 2000 mg/dL, and no secondary causes of hypertriglyceridemia. MAIN OUTCOME MEASURES: Genotyping and phenotypic features. RESULTS: Four patients harbored homozygous or compound heterozygous mutations in LPL, 3 had homozygous mutations in GPIHBP1, and 1 had a heterozygous APOA5 mutation. We failed to fully identify the genetic etiology in 2 cases: 1 had a heterozygous LPL mutation only and another did not have any mutations. We identified 2 interesting phenotypic features: the patient with heterozygous APOA5 mutation normalized triglyceride levels with weight loss and fish oil therapy, and all 7 female patients were anemic. CONCLUSIONS: Our data suggest the possibility of novel loci for T1HLP. We observed that heterozygous APOA5 mutation can cause T1HLP but such patients may unexpectedly respond to therapy, and females with T1HLP suffer from anemia. Further studies of larger cohorts may elucidate more phenotype-genotypes relationships among T1HLP subtypes. Published by Elsevier Inc. on behalf of National Lipid Association.
* Corresponding author. E-mail address: [email protected] Submitted October 2, 2013; revised January 7, 2014. Accepted for publication February 12, 2014.
Type I hyperlipoproteinemia (T1HLP, OMIM# 238600, also called familial chylomicronemia syndrome) is a rare, autosomal recessive disorder characterized by severe elevations in circulating triglycerides (TG) resulting from
1933-2874/$ - see front matter Published by Elsevier Inc. on behalf of National Lipid Association. http://dx.doi.org/10.1016/j.jacl.2014.02.006
288 accumulation of TG-rich lipoproteins, especially chylomicrons. Patients present with several physical findings: eruptive or tuberous xanthomas, lipemia retinalis, and hepatosplenomegaly. More concerning, severe hypertriglyceridemia predisposes to acute pancreatitis,1,2 a serious condition often complicated by the systemic inflammatory response syndrome, multiorgan failure, pancreatic necrosis, and mortality rates as high as 20%.3,4 T1HLP results from defects in the breakdown of chylomicrons, primarily due to deficiency of lipoprotein lipase (LPL). LPL binds to heparan sulfate, located at the heparin-binding site on the surface of capillary endothelial cells, allowing LPL to extend into the plasma and participate in the hydrolysis of TG carried in chylomicrons and very-low-density lipoproteins.5 More than 220 diseasecausing LPL mutations have been reported in more than 500 patients. Besides LPL, several additional loci have been identified for T1HLP, all of which encode for either cofactors or proteins involved in LPL’s maturation or binding to endothelium: apolipoprotein CII (APOC2),6 lipase maturation factor 1 (LMF1),7 glycosyl-phosphatidylinositol anchored high-density lipoprotein-binding protein 1 (GPIHBP1),8,9 and apolipoprotein AV (APOA5).10–13 APOC2 is synthesized in the liver and subsequently secreted into the plasma. APOC2 is found on high-density lipoproteins (HDL), chylomicrons, and very-low-density lipoproteins, and acts as an activator for LPL. LMF1 serves as a chaperone of the endoplasmic reticulum and is required for the posttranslational activation of LPL by dimerizing inactive monomers of LPL into active enzymes.14 GPIHBP1 is a capillary endothelial protein that transports LPL into capillaries15 and provides a platform for LPL-mediated hydrolysis of chylomicrons.16 APOA5 plays a role in reducing triglycerides, most likely by stimulating LPL.17 Mutations in other loci besides LPL are found infrequently in patients with T1HLP. Our review of the literature reveals only 20 families with disease-causing mutations in APOC218–33; 12 families with GPIHBP1 mmtations15,16,34; 2 patients with LMF1 mmtations7,35; and 5 patients with homozygous mutations in APOA5.10–13 We lack data on whether subtle phenotypic variations exist in patients with the various genetic subtypes of T1HLP. Therefore, we carefully evaluated our patients with T1HLP and ascertained their genotype-phenotype relationships.
Materials and methods All patients or their legal guardians gave written informed consent, and the Institutional Review Board of the University of Texas Southwestern Medical Center approved the protocol. T1HLP patients were ascertained from specialty lipid clinics in the Dallas, TX, area. Inclusion criteria consisted of a history of chylomicronemia with serum TG levels above 2000 mg/dL. We excluded patients with hypertriglyceridemia resulting from a secondary
Journal of Clinical Lipidology, Vol 8, No 3, June 2014 cause such as diabetes mellitus (if it was diagnosed before onset of hypertriglyceridemia and pancreatitis), alcoholism, renal insufficiency, untreated hypothyroidism, or the use of estrogen or other medications. Detailed personal and family history regarding hypertriglyceridemia, pancreatitis, medication use, and xanthomas was obtained. Patients were examined for the presence of lipemia retinalis and eruptive or tuberous xanthomas.
Candidate gene analysis Genomic DNA was isolated from whole blood using the Easy-DNA kit (Invitrogen, Carlsbad, CA). All exons and the flanking intronic regions of LPL, APOC2, GPIHBP1, LMF1, and APOA5 were amplified and sequenced using Applied Biosystems’ 3730xl DNA Analyzer (Applied Biosystems, Carlsbad, CA). The genes were sequenced sequentially: LPL, APOC2, GPIHBP1, LMF1, and then APOA5.
Lipids and lipoproteins Medical charts were reviewed to obtain historic lipid levels. All centers measured fasting total cholesterol, TG, and HDL-cholesterol (HDL-C) using enzymatic assays in commercial laboratories.
Results Ten patients with T1HLP were evaluated (Fig. 1, Table 1). Of these, 7 were female and 3 were male. The mean age of our patients was 32.6 years (range, 5 to 45 years). The age at time of diagnosis varied from infancy to the early 30s with a mean age of 12.5 years; however, most patients had some symptoms in childhood. Only 1 patient had a history of parental consanguinity. A history of acute pancreatitis was a common finding among our patients. Although 1 patient with a confirmed mutation in LPL had no history of pancreatitis, he had chronic, recurring abdominal pain since childhood. Three of our patients have had 1 episode of acute pancreatitis, and the remaining 6 have had multiple episodes (up to 15) of pancreatitis. The mean body mass index (BMI) was 26.1 kg/m2. Four patients had hepatosplenomegaly. The mean total cholesterol level was 310 mg/dL, fasting serum triglyceride level was 3252 mg/dL, and HDL-C level was 21 mg/dL (Table 2). All patients had a history of fasting serum TG levels above 2000 mg/dL. The mean hemoglobin concentration was 11.2 g/dL, and all 7 female patients were anemic. Genetic testing revealed 4 patients with disease-causing variants in LPL (3 with homozygous mutations and 1 with compound heterozygous mutations), 1 patient with a heterozygous LPL mutation, 3 patients with homozygous GPIHBP1 mutations, 1 patient with a heterozygous APOA5 mutation, and 1 patient without any diseasecausing mutations.
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Figure 1 Pedigrees of our patients with type 1 hyperlipoproteinemia. Squares, males; circles, females; filled symbols, affected subjects; open symbols, unaffected subjects; diagonal line, deceased subject; arrow, proband; double horizontal line, consanguineous marriage.
Case reports Case 1 (T1HLP 1.7) This 36-year-old Asian Indian female was first diagnosed with a lipid disorder at the age of 1 year. During childhood, she recalled multiple episodes of abdominal pain and experienced around 2 episodes of acute pancreatitis per year from the ages of 6 to 16 years. Subsequently, for a 10-year period, she experienced no episodes of acute pancreatitis. At age 26 years, during her first pregnancy, she again developed acute pancreatitis requiring hospitalization. Since that time, she has had at least 5 hospitalizations for acute pancreatitis. There was no known consanguinity among the parents. She had no history of diabetes, estrogen use, or alcohol use. Her brother was known to have elevated serum triglycerides, but not exceeding 1000 mg/dL. On examination, she had lipemia retinalis and hepatosplenomegaly with the liver palpable 4 cm below the right costal margin. She had no xanthomas. The highest fasting serum triglyceride level at our institution was 2476 mg/dL; however, she recalls serum triglyceride levels of 9000 to 10,000 mg/dL in the past. She was
also anemic with a hemoglobin concentration of 9.7 g/dL and a mean corpuscular volume (MCV) of 81 fL. Her liver function tests were normal. The patient was found to have a homozygous mutation in LPL (c.IVS211G.A). She was asked to follow an extremely low-fat diet, and her triglyceride levels decreased; however, they remain higher than 1000 mg/dL.
Case 2 (T1HLP 2.4) This 21-year-old Asian Indian female was first noted to have high triglycerides at 1 month of age. She had been hospitalized for acute pancreatitis 3 times; however, she had bouts of abdominal pain since childhood, which occurred about once a month with the ingestion of a high-fat meal. She did not follow any particular diet, but had learned to avoid fatty foods. She had no history of estrogen or alcohol use, and no history of diabetes. There was no known consanguinity among her parents. Her medications at the initial visit included fenofibrate 134 mg/day and fish oil 1 capsule daily. She was a thin young female with pale conjunctiva, lipemia retinalis, and mild hepatosplenomegaly. She had no eruptive xanthomas.
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Table 1
Demographic and clinical features of patients with type 1 hyperlipoproteinemia Mutation
Case #
Age/ethnicity/sex
Age of onset
BMI (kg/m2)
gene
Het/Hom
Nucleotide
Protein
1 2
36/Indian/F 21/Indian/F
1 year 1 month
28.1 19.2
LPL LPL
3 4
42/Indian/M 44/Hispanic/F
29 years 25 years
20.2 31.6
LPL LPL
hom het het hom hom
IVS211G.A 721C.T IVS112insT IVS1-1G.C 1051G.A
— P241S — — G351R
5 6 7 8 9
40/El Salvadorian/F 5/Indian/M 29/Mexican/F 45/Caucasian/F 45/Colombian/F
24 years 2 months 23 years 10 years 13 years
25.8 * 28.4 26.4 35.6
GPIHBP1 GPIHBP1 APOA5 LPL —
hom hom het het
203G.A del 289C.T 644G.A —
C68Y del Q97X G215E —
10
19/Indian/M
2 months
19.8
GPIHBP1
hom
del
del
Pancreatitis, # of episodes
HSM
Anemia
Lipid-lowering drugs tried
Response to fibrates/fish oil
15 3
Yes Yes
Yes Yes
Fish oil, gemfibrozil Fenofibrate, fish oil
No No
0 1
No No
No Yes
No No
.10 1 2 2 7
Yes No No No Yes
Yes No Yes Yes Yes
1
No
No
Fish oil Fenofibrate, fish oil, niacin, simvastatin Fish oil, gemfibrozil None Fish oil Fenofibrate, fish oil Fenofibrate, fish oil, rosuvastatin None
No Yes No No -
BMI, body mass index; Het, heterozygous; Hom, homozygous; HSM, hepatosplenomegaly. *3rd percentile for weight.
Laboratory values for patients with type 1 hyperlipoproteinemia
Case #
Total cholesterol (mg/dL)
Triglycerides (mg/dL)
HDL-C (mg/dL)
Hgb (g/dL)
Hct (%)
MCV (fL)
Iron (mg/dL)
1 2 3 4 5 6 7 8 9 10
197 255 344 269 600 177 235 441 462 121
2476 3090 4840 1522 1960 1578 2000 4120 5790 1140
17 23 41 16 18 11 26 37 12 13
9.7 8.9 13.2 10.9 8.8 12.7 11.2 8.6 10.6 17.2
30.3 28.7 39.5 31.3 28.0 35.7 33.7 29.8 29.1 48.3
81 83.4 83.9 85.8 73.7 81.3 75.2 82.1 85.6 86.9
58 69 102 42 39 81 20 39 47 117
TIBC (mg/dL)
Ferritin (ng/mL)
69*
86*
398 509
30 20
335
81
AST (U/L)
ALT (U/L)
Menses
20 23 58 20 21 29 84 31 16 24
10 12 34 17 13 14 85 34 12 24
N H Male H H Male N H ## Male
##, hysterectomy age 27 years; ALT, alanine aminotransferase; AST, aspartate aminotransferase; H, heavy flow; Hct, hematocrit; HDL-C, high-density lipoprotein cholesterol; Hgb, hemoglobin; MCV, mean corpuscular volume; N, normal flow; TIBC, total iron-binding capacity. Normal ranges: Hemoglobin male 13.2–17.1 g/dL, hemoglobin female 11.7–15.5 g/dL; hematocrit male 38.5–50%, hematocrit female 35–45%; MCV 80–100 fL; iron male 45–170 mg/dL, iron female 40– 175 mg/dL; AST 10–30 U/L; ALT 6–40 U/L; TIBC 149–491 mg/dL (*271–448 mg/dL); ferritin 13–150 ng/mL (*10–143 ng/mL).
Journal of Clinical Lipidology, Vol 8, No 3, June 2014
Table 2
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The highest serum triglyceride level at our institution was .4425 mg/dL; however, her father recalled a triglyceride level around 19,000 mg/dL in the past. She was also noted to have a chronic normocytic anemia, with a hemoglobin concentration of 8.9 g/dL and MCV of 83.4 fL. She had compound heterozygous mutations in LPL (c.721C.T [p.P241S] and c.IVS112insT). Because fish oil and fenofibrate did not result in a reduction of triglyceride levels, they were discontinued. She was started on orlistat 120 mg orally 3 times a day in an attempt to reduce fat absorption from the diet. The patient believes that her attacks of abdominal pain have decreased in frequency since starting orlistat. Her serum triglycerides have ranged from 667 to 1803 mg/dL. She has some oily stools with the medication, but is able to tolerate it.
Case 3 (T1HLP 3.12) This 42-year-old Asian Indian male was first noted to have high triglycerides at around age 29 years during a routine blood test. On direct questioning, he recalled many episodes of abdominal pain as a child, but denied hospitalizations for acute pancreatitis and could not recall having eruptive xanthomas. He drank alcohol only occasionally (1 to 2 beers on weekends). He had a history of hypothyroidism that was adequately treated with levothyroxine. There was no history of consanguinity between his parents, and he had no history of diabetes. He was a thin male with lipemia retinalis on funduscopic examination, but he had no hepatosplenomegaly or xanthomas. His serum triglyceride levels had been as high as 4840 mg/dL. He had a homozygous LPL mutation (c.IVS1-1G.C). He was placed on omega-3-acid ethyl esters 2 capsules twice a day and asked to follow a very low-fat diet. His serum triglycerides remain about 2000 mg/dL.
Case 4 (T1HLP 4.12) This 44-year-old Hispanic female was first noted to have high triglycerides during pregnancy at age 25 years. She had had 1 episode of pancreatitis that required hospitalization at age 38 years. She denied a history of estrogen use. She denied alcohol use but was consuming a white winegarlic drink. She had hypothyroidism, adequately treated with levothyroxine, and no history of diabetes. Her father and mother were first cousins. She had been taking fenofibrate 200 mg daily, fish oil 3 capsules daily, simvastatin 40 mg daily, and niacin 500 mg daily for more than 10 years. She had a BMI of 31.6 kg/m2 and also had lipemia retinalis. She had no acanthosis nigricans, hepatosplenomegaly, or xanthomas. Her triglycerides were elevated up to 3675 mg/dL despite compliance with her medications. She was found to have a normocytic anemia with a hemoglobin concentration of 10.9 g/dL. She had a homozygous mutation in LPL (c.1051G.A [p.G351R]). She was asked to follow an extremely low-fat diet and discontinue the
291 white wine-garlic drink. Her serum triglycerides improved, but remain just above 1000 mg/dL.
Case 5 (T1HLP 5.9) This previously reported 40-year-old El Salvadorian female was first diagnosed with hypertriglyceridemia during pregnancy at age 24 years.34 She had experienced intermittent abdominal pain since childhood, and had numerous hospitalizations resulting from acute pancreatitis. She noted that her abdominal pain improved by avoidance of fat in her diet. She denied the use of estrogen. She had no history of diabetes and no history of consanguinity among the parents. One of her brothers had T1HLP and a history of acute pancreatitis. She had been taking gemfibrozil 600 mg twice a day and fish oil 1 g 3 times a day for 1 year. Her BMI was 25.8 kg/m2. She had hepatosplenomegaly and was noted to have eruptive xanthomas on her elbows. There was no lipemia retinalis. The maximum triglyceride levels were 9600 mg/dL. She was anemic with a hemoglobin concentration of 8.8 g/dL and MCV of 73.7 fL. She had a homozygous mutation in GPIHBP1 (c.203G.A [p.C68Y]). She was asked to follow a low-fat diet and her TG level improved; however, it remains higher than 1000 mg/dL.
Case 6 (T1HLP 6.31) This previously reported 5-year-old Asian Indian boy initially presented at 2 months of age.34 At that time, he presented with lethargy and anemia, and was noted to have ‘‘strawberry-pink’’ blood. His serum triglyceride level was found to be .20,000 mg/dL. His hospital course was complicated by shock and severe anemia requiring intensive care. His mother recalled that he had pancreatitis while in the intensive care unit, but there was no clear mention of it in the hospital records. He had no further episodes of pancreatitis. He occasionally had reddish bumps on his buttocks, and occasionally had postprandial abdominal pain. He followed a low-fat diet. Both parents were from Gujarat, India; however, there was no known history of consanguinity. The patient had a distant aunt on his mother’s side and a distant cousin on his father’s side (case 10) who also had T1HLP. He was at the 25th percentile for height and 3rd percentile for weight. He had lipemia retinalis on funduscopic examination and a grade II/VI systolic murmur loudest at the apex. He had no hepatosplenomegaly or eruptive xanthomas. He had a homozygous mutation causing a deletion of the entire GPIHBP1 gene.34 His triglycerides remain elevated at 2000 mg/dL.
Case 7 (T1HLP 7.8) This 29-year-old Mexican female was first diagnosed with hypertriglyceridemia at age 23 years. She recalled intermittent abdominal pain with nausea and vomiting in
292 her teenage years. She also recalled yellow-red bumps that appeared on her back and flexor surface of her knees during those years but never required hospitalization in childhood. At ages 24 and 26, though, she was hospitalized for acute pancreatitis resulting from hypertriglyceridemia. She reported abdominal pain following ingestion of fatty foods. She had no history of diabetes or estrogen or steroid use. She did not drink alcohol, and there was no parental consanguinity. Her maternal grandmother had a history of pancreatitis, but it is unknown if she had high triglycerides. Her BMI was 28.4 kg/m2. She had hepatomegaly, but no acanthosis nigricans or xanthomas. Her serum triglycerides were elevated to 2000 mg/dL. Genetic testing found no mutation in LPL, APOC2, GPIHBP1, or LMF1. However, she had a heterozygous mutation in APOA5 (c.289C.T [p.Q97X]). She was started on fish oil 12 capsules daily. She lost 6 kg of weight, and eventually her triglyceride levels decreased to 71 mg/dL.
Case 8 (T1HLP 8.3) This 45-year-old white female was first noted to have high triglycerides at age 10 or 11 years. She recalled taking gemfibrozil as a teenager and noted that her blood was ‘‘white’’ and ‘‘milky.’’ She had had 2 episodes of acute pancreatitis in the past; the first episode was during her first pregnancy at age 28 years and the second at age 36 years. She did not recall chronic abdominal pain or skin rashes. She took an oral contraceptive pill briefly when she was first married, but not otherwise. She did not drink alcohol and did not have diabetes. She was taking fenofibric acid 135 mg daily. She was also prescribed fish oil 2 capsules twice a day, but was not taking this consistently. Her BMI was 26.4 kg/m2. Lipemia retinalis was noted on funduscopy. There was no acanthosis nigricans, organomegaly, or eruptive xanthomas. Her fasting serum triglyceride level was 4120 mg/dL, HbA1c was 5.4%, and she had a normocytic anemia with a hemoglobin concentration of 8.6 g/dL and MCV of 82.1 fl. She had a heterozygous mutation in LPL (c.644G.A [p.G215E]). No mutations were found in APOC2, GPIHBP1, LMF1, and APOA5.
Case 9 (T1HLP 9.8) This 45-year-old Colombian female was first diagnosed with hypertriglyceridemia at age 13 years. She had the first episode of pancreatitis at age 21 years during her first pregnancy and subsequently had 6 more episodes. She developed diabetes at age 39 years, which was controlled with insulin. She had a history of coronary artery disease (CAD) with stent placement at age 42 years. She took oral contraceptive pills on and off in her 20s. She did not drink alcohol, and there was no history of consanguinity among the parents. Her BMI was 35.6 kg/m2. She did not have xanthomas or lipemia retinalis, but had mild hepatomegaly and splenomegaly. Her triglyceride level was 5790 mg/dL
Journal of Clinical Lipidology, Vol 8, No 3, June 2014 and HbA1c was 7%. She was anemic with a hemoglobin concentration of 10.6 g/dL and MCV of 85.6 fL. Genotyping for LPL, APOC2, GPIHBP1, LMF1, and APOA5 revealed no disease-causing variants.
Case 10 (T1HLP 6.29) This 19-year-old Asian Indian male was first noted to have high triglycerides as an infant. At age 2 months, he presented with a fever and was found to have a triglyceride level of w25,000 mg/dL. He had an episode of pancreatitis at age 2. Since then, he has had bouts of abdominal pain, especially after eating seafood and high-fat foods. The abdominal pain was occasionally associated with nausea, vomiting, and diarrhea. When he followed an extremely low-fat diet, he noted fewer episodes of abdominal pain. He had no other medical conditions and no history of diabetes or alcohol use. He took no medications. His parents were distantly related, and the patient had a distant cousin with T1HLP (case 6). He was thin with a BMI of 19.8 kg/m2. There was no lipemia retinalis on funduscopic examination. He had no hepatosplenomegaly or xanthomas. His triglyceride level was 1140 mg/dL. He was not anemic, and his liver function tests were normal. Genetic testing revealed the same large, homozygous deletion of GPIHBP1 as reported previously.34
Discussion Our case series suggests that LPL deficiency is the most prevalent cause of T1HLP, followed by other extremely rare subtypes with GPIHBP1 deficiency and APOA5 mutation. No patient had a mutation in APOC2 or LMF1. Furthermore, in 2 patients, we were unable to fully explain the phenotype based on the results of genetic testing, suggesting further genetic heterogeneity and the possibility of novel loci for T1HLP. Case 9 developed hypertriglyceridemia during childhood, and although she developed diabetes, it was not until after she suffered from multiple episodes of acute pancreatitis. Although we cannot exclude the remote possibility of a small deletion or promoter/intronic mutation in the known T1HLP genes, her case suggests the possibility of an undiscovered T1HLP locus. Case 8 harbored only a heterozygous mutation in LPL. Heterozygous LPL mutations result in decreased LPL activity and mass, mild combined hyperlipidemia, and reduced HDL-C.36 Only in the presence of secondary factors (eg, uncontrolled diabetes, heavy alcohol intake, estrogen therapy), do subjects with heterozygous LPL mutations develop type 5 hyperlipoproteinemia. However, the clinical presentation in case 8 resembles the other T1HLP cases more so than type 5 hyperlipoproteinemia—specifically, she lacked any secondary factors. Thus, either we failed to identify a second LPL mutation on Sanger sequencing or she harbors a mutation in an undiscovered T1HLP locus.
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T1HLP occurs with homozygous APOA5 mutations, but case 7 harbored only a heterozygous APOA5 mutation. Patients with heterozygous APOA5 mutations have previously been reported to display variable serum triglyceride levels, ranging from mild to extremely high levels without a secondary cause.10–13 Our patient clinically presented with T1HLP; however, her TG levels improved with fish oil and weight loss. This is in contrast to all the other patients with LPL or GPIHBP1 deficiency who continued to have extremely high TG concentrations despite fibrates and/or fish oil therapy. LPL deficiency should result in a lack of TG storage in adipose tissue—a ‘‘lipodystrophic’’ phenotype. Yet, most of our patients were overweight (BMI range 19.2–35.6 kg/m2) with a normal fat distribution; BMI did not differ by T1HLP etiology. These findings suggest alternative adipocyte-specific lipases that may be upregulated in the absence of LPL or its cofactors. Anemia has been previously reported in a case series of infants presenting with T1HLP37; 7 of 16 infants presented with a normocytic anemia resulting from an unknown cause, and both male and female infants were affected. Reports of T1HLP adults with anemia are scarce. In our female patients, hemoglobin concentration ranged from 8.6 to 10.9 g/dL (Table 2). The serum iron level was also found to be low in nearly all females. The anemia in these patients was chronic, and the hemoglobin concentrations did not seem to correlate with serum TG levels. The red blood cell MCV was low to low-normal in these patients, suggesting iron deficiency or anemia of chronic disease. The possibility of artifactual reduction of hematocrit resulting from severe chylomicronemia was considered, but it is less likely because our male patients lacked anemia despite similar hypertriglyceridemia. Of our female patients, 4 had menorrhagia, 2 had normal menstrual periods, and 1 had a hysterectomy. Serum ferritin and total ironbinding capacity were measured in 3 patients with menorrhagia and 2 of them were confirmed to have iron deficiency anemia. The etiology of the anemia remains unclear. Possible explanations include bone marrow suppression, splenic sequestration, menorrhagia, or spurious values in the setting of chylomicronemia. The relationship between chylomicronemia and premature cardiovascular disease remains controversial. Only 1 patient suffered from CAD (case 9), and she had developed diabetes before the diagnosis of CAD. Although most cases of T1HLP in the literature are not associated with the development of CAD, there have been case reports of patients with LPL mutations who developed premature atherosclerosis.38,39 Two patients with GPIHBP1 mutations and CAD have been reported as well.8,40 No clear mechanism for the development of atherosclerosis in these patients has been elucidated from the reports. The management of T1HLP is challenging for absence of any clinical trials of lipid-lowering drugs. Our
293 experience and previous anecdotal reports suggest that the current TG lowering agents—niacin, fibrates, and fish oil— are ineffective, and despite these therapies, patients continue to have episodes of abdominal pain and acute pancreatitis. The only option is to drastically reduce their fat intake to 10% to 15% of total energy to minimize chylomicron formation. This extremely low-fat diet may reduce serum TG levels to less than 2000 mg/dL (as in cases 1, 3, 4, 5, and 10), greatly mitigating the risk of acute pancreatitis, although the durability and feasibility of this extreme diet remains unknown. Heparin has been investigated as a therapeutic option for T1HLP patients with GPIHBP1 mutations, but reports are conflicting. Heparin administration reduced TG levels in GPIHBP1-deficient mice,41 and in 1 young boy, a 6-hour heparin infusion markedly reduced TG levels.42 Additional human studies, however, failed to show a reduction in plasma TG upon heparin administration to GPIHBP1deficient patients.34,42,43 Thus, unfortunately, low-dose heparin therapy may not be of therapeutic benefit to those with GPIHBP1 deficiency. The European Commission recently approved an LPL gene therapy called alipogene tiparvovec, which is composed of the LPL gene along with an adeno-associated virus subtype 1 (AAV1) vector (AAV1-LPLS447x).44 A study of alipogene tiparvovec in patients with LPL deficiency showed an initial reduction in serum TG by 40%, although TG returned to baseline by month 6 despite clear long-term transgene expression.44 Still, patients reported improvement in quality of life and an overall reduction of the incidence of acute pancreatitis and/or intensity of the crisis. However, alipogene tiparvovec may not be useful for T1HLP patients with mutations in APOC2, APOA5, LMF1, and GPIHBP1. Other potential therapeutic options in T1HLP patients are under investigation, such as an intestinal lipase inhibitor, orlistat; a diacylglycerol acyltransferase inhibitor, LCQ908; an intestinal-specific microsomal triglyceride transfer protein 1 inhibitor, SLx-4090; and an APOC3 inhibitor. In summary, our data suggest further genetic heterogeneity in T1HLP with the possibility of novel loci. Furthermore, understanding of phenotypic differences among various subtypes of T1HLP will require careful phenotyping of larger cohorts of patients belonging to each subtype.
Acknowledgments We thank Sarah Masood and Tommy Hyatt for technical assistance and Claudia Quittner for study coordination. The study was supported by the Southwest Medical Foundation. Disclosure Statement: A.G. is a consultant and on the advisory board for Pfizer and Bristol-Myers-Squibb, speaker for Merck, and a consultant for Aegerion. Z.A. is on the speaker’s bureau for Sanofi-Aventis and attended an advisory board for Aegerion Pharmaceuticals. N.C. and S.B. have nothing to disclose.
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References 1. Brunzell JD. Clinical practice. Hypertriglyceridemia. N Engl J Med. 2007;357:1009–1017. 2. Fortson MR, Freedman SN, Webster PD 3rd. Clinical assessment of hyperlipidemic pancreatitis. Am J Gastroenterol. 1995;90:2134–2139. 3. Banks PA, Freeman ML. Practice guidelines in acute pancreatitis. Am J Gastroenterol. 2006;101:2379–2400. 4. Gloor B, Muller CA, Worni M, Martignoni ME, Uhl W, Buchler MW. Late mortality in patients with severe acute pancreatitis. Br J Surg. 2001;88:975–979. 5. Cheng CF, Oosta GM, Bensadoun A, Rosenberg RD. Binding of lipoprotein lipase to endothelial cells in culture. J Biol Chem. 1981;256: 12893–12898. 6. Brunzell JD, Deeb SS. Familial lipoprotein lipase deficiency, Apo C-II deficiency, and hepatic lipase deficiency. In: Scriver CR, Beaudet BL, Sly WS, Valle D, editors. The Metabolic and Molecular Bases of Inherited Disease. New York: The McGraw-Hill Companies, 2006. 7. Peterfy M, Ben-Zeev O, Mao HZ, et al. Mutations in LMF1 cause combined lipase deficiency and severe hypertriglyceridemia. Nat Genet. 2007;39:1483–1487. 8. Wang J, Hegele RA. Homozygous missense mutation (G56R) in glycosylphosphatidylinositol-anchored high-density lipoproteinbinding protein 1 (GPI-HBP1) in two siblings with fasting chylomicronemia (MIM 144650). Lipids Health Dis. 2007;6:23. 9. Beigneux AP, Franssen R, Bensadoun A, et al. Chylomicronemia with a mutant GPIHBP1 (Q115P) that cannot bind lipoprotein lipase. Arterioscler Thromb Vasc Biol. 2009;29:956–962. 10. Priore Oliva C, Carubbi F, Schaap FG, Bertolini S, Calandra S. Hypertriglyceridaemia and low plasma HDL in a patient with apolipoprotein A-V deficiency due to a novel mutation in the APOA5 gene. J Intern Med. 2008;263:450–458. 11. Marcais C, Verges B, Charriere S, et al. Apoa5 Q139X truncation predisposes to late-onset hyperchylomicronemia due to lipoprotein lipase impairment. J Clin Invest. 2005;115:2862–2869. 12. Priore Oliva C, Pisciotta L, Li Volti G, et al. Inherited apolipoprotein A-V deficiency in severe hypertriglyceridemia. Arterioscler Thromb Vasc Biol. 2005;25:411–417. 13. Priore Oliva C, Tarugi P, Calandra S, et al. A novel sequence variant in APOA5 gene found in patients with severe hypertriglyceridemia. Atherosclerosis. 2006;188:215–217. 14. Peterfy M. Lipase maturation factor 1: a lipase chaperone involved in lipid metabolism. Biochim Biophys Acta. 2012;1821:790–794. 15. Davies BS, Beigneux AP, Barnes RH 2nd, et al. GPIHBP1 is responsible for the entry of lipoprotein lipase into capillaries. Cell Metab. 2010;12:42–52. 16. Beigneux AP, Davies BS, Gin P, et al. Glycosylphosphatidylinositolanchored high-density lipoprotein-binding protein 1 plays a critical role in the lipolytic processing of chylomicrons. Cell Metab. 2007;5: 279–291. 17. Nilsson SK, Heeren J, Olivecrona G, Merkel M. Apolipoprotein A-V: a potent triglyceride reducer. Atherosclerosis. 2011;219:15–21. 18. Baggio G, Manzato E, Gabelli C, et al. Apolipoprotein C-II deficiency syndrome. Clinical features, lipoprotein characterization, lipase activity, and correction of hypertriglyceridemia after apolipoprotein C-II administration in two affected patients. J Clin Invest. 1986;77: 520–527. 19. Beil FU, Fojo SS, Brewer HB Jr., Greten H, Beisiegel U. Apolipoprotein C-II deficiency syndrome due to apo C-IIHamburg: clinical and biochemical features and HphI restriction enzyme polymorphism. Eur J Clin Invest. 1992;22:88–95. 20. Breckenridge WC, Alaupovic P, Cox DW, Little JA. Apolipoprotein and lipoprotein concentrations in familial apolipoprotein C-II deficiency. Atherosclerosis. 1982;44:223–235.
Journal of Clinical Lipidology, Vol 8, No 3, June 2014 21. Breckenridge WC, Little JA, Steiner G, Chow A, Poapst M. Hypertriglyceridemia associated with deficiency of apolipoprotein C-II. N Engl J Med. 1978;298:1265–1273. 22. Cox DW, Breckenridge WC, Little JA. Inheritance of apolipoprotein C-II deficiency with hypertriglyceridemia and pancreatitis. N Engl J Med. 1978;299:1421–1424. 23. Fellin R, Baggio G, Poli A, et al. Familial lipoprotein lipase and apolipoprotein C-II deficiency. Lipoprotein and apoprotein analysis, adipose tissue and hepatic lipoprotein lipase levels in seven patients and their first degree relatives. Atherosclerosis. 1983;49: 55–68. 24. Fojo SS, Baggio G, Gabelli C, et al. Apolipoprotein C-II deficiency: identification of a structural variant ApoC-II Padova. Biochem Biophys Res Commun. 1988;154:73–79. 25. Fojo SS, de Gennes JL, Chapman J, et al. An initiation codon mutation in the apoC-II gene (apoC-II Paris) of a patient with a deficiency of apolipoprotein C-II. J Biol Chem. 1989;264: 20839–20842. 26. Fojo SS, Lohse P, Parrott C, et al. A nonsense mutation in the apolipoprotein C-IIPadova gene in a patient with apolipoprotein C-II deficiency. J Clin Invest. 1989;84:1215–1219. 27. Fojo SS, Stalenhoef AF, Marr K, Gregg RE, Ross RS, Brewer HB Jr. A deletion mutation in the ApoC-II gene (ApoC-II Nijmegen) of a patient with a deficiency of apolipoprotein C-II. J Biol Chem. 1988; 263:17913–17916. 28. Kawano M, Kodama K, Inadera H, et al. A case of apolipoprotein C-II deficiency with coronary artery disease. Clin Exp Med. 2002;2: 29–31. 29. Ohno M, Ishibashi S, Nakao K, et al. A neonatal case of apolipoprotein C-II deficiency. Eur J Pediatr. 1989;148:550–552. 30. Okubo M, Hasegawa Y, Aoyama Y, Murase T. A G11 to C mutation in a donor splice site of intron 2 in the apolipoprotein (apo) C-II gene in a patient with apo C-II deficiency. A possible interaction between apo C-II deficiency and apo E4 in a severely hypertriglyceridemic patient. Atherosclerosis. 1997;130:153–160. 31. Takase S, Osuga J, Fujita H, et al. Apolipoprotein C-II deficiency with no rare variant in the APOC2 gene. J Atheroscler Thromb. 2013;20: 481–493. 32. Wilson CJ, Priore Oliva C, Maggi F, Catapano AL, Calandra S. Apolipoprotein C-II deficiency presenting as a lipid encephalopathy in infancy. Ann Neurol. 2003;53:807–810. 33. Yamamura T, Sudo H, Ishikawa K, Yamamoto A. Familial type I hyperlipoproteinemia caused by apolipoprotein C-II deficiency. Atherosclerosis. 1979;34:53–65. 34. Rios JJ, Shastry S, Jasso J, et al. Deletion of GPIHBP1 causing severe chylomicronemia. J Inherit Metab Dis. 2012;35:531–540. 35. Cefalu AB, Noto D, Arpi ML, et al. Novel LMF1 nonsense mutation in a patient with severe hypertriglyceridemia. J Clin Endocrinol Metab. 2009;94:4584–4590. 36. Babirak SP, Iverius PH, Fujimoto WY, Brunzell JD. Detection and characterization of the heterozygote state for lipoprotein lipase deficiency. Arteriosclerosis. 1989;9:326–334. 37. Feoli-Fonseca JC, Levy E, Godard M, Lambert M. Familial lipoprotein lipase deficiency in infancy: clinical, biochemical, and molecular study. J Pediatr. 1998;133:417–423. 38. Benlian P, De Gennes JL, Foubert L, Zhang H, Gagne SE, Hayden M. Premature atherosclerosis in patients with familial chylomicronemia caused by mutations in the lipoprotein lipase gene. N Engl J Med. 1996;335:848–854. 39. Saika Y, Sakai N, Takahashi M, et al. Novel LPL mutation (L303F) found in a patient associated with coronary artery disease and severe systemic atherosclerosis. Eur J Clin Invest. 2003;33: 216–222. 40. Yamamoto H, Onishi M, Miyamoto N, et al. Novel combined GPIHBP1 mutations in a patient with hypertriglyceridemia associated with CAD. J Atheroscler Thromb. 2013;20:777–784.
Chokshi et al
Type 1 hyperlipoproteinemia
41. Weinstein MM, Yin L, Beigneux AP, et al. Abnormal patterns of lipoprotein lipase release into the plasma in GPIHBP1-deficient mice. J Biol Chem. 2008;283:34511–34518. 42. Franssen R, Young SG, Peelman F, et al. Chylomicronemia with low postheparin lipoprotein lipase levels in the setting of GPIHBP1 defects. Circ Cardiovasc Genet. 2010;3:169–178.
295 43. Olivecrona G, Ehrenborg E, Semb H, et al. Mutation of conserved cysteines in the Ly6 domain of GPIHBP1 in familial chylomicronemia. J Lipid Res. 2010;51:1535–1545. 44. Gaudet D, Methot J, Dery S, et al. Efficacy and long-term safety of alipogene tiparvovec (AAV1-LPL(S447X)) gene therapy for lipoprotein lipase deficiency: an open-label trial. Gene Ther. 2013;20:361–369.
