J Nephrol DOI 10.1007/s40620-014-0073-0
CASE REPORT
A novel homozygous GLUT9 mutation cause recurrent exerciseinduced acute renal failure and posterior reversible encephalopathy syndrome Li-jun Mou • Lan-ping Jiang • Ying Hu
Received: 22 October 2013 / Accepted: 19 February 2014 Ó Italian Society of Nephrology 2014
Abstract Renal hypouricemia (RHU) is an autosomal recessive hereditary disease characterized by impaired renal urate reabsorption and subsequent profound hypouricemia. There are two types of RHU, type 1 and type 2, caused by the loss-of-function mutation of SLC22A12 and SLC2A9 genes, respectively. RHU predisposes affected people to exercise-induced acute renal failure (EIARF), posterior reversible encephalopathy syndrome (PRES) and nephrolithiasis. A Chinese patient had experienced three episodes of EIARF and one episode of PRES. The investigations showed profound hypouricemia and significantly increased renal excretion of UA. Cranial magnetic resonance imaging showed communicating hydrocephalus. Renal biopsy displayed interlobular artery intimal thickening with reduction of lumen and acute tubulointerstitial injury. The mutational analysis revealed a homozygous splice-site mutation in the SLC2A9 gene encoding glucose transporter 9. The patient was diagnosed as RHU type 2 caused by a loss-of-function mutation of the SLC2A9 gene. Consequently, he was strictly prohibited from strenuous exercise. During the 5-year follow-up, EIARF and PRES never recurred. Strenuous exercise may induce systemic (including renal and cerebrovascular) vasoconstriction
L. Mou Y. Hu (&) Department of Nephrology, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Jiefang Rd 88, Hangzhou 31009, China e-mail: [email protected] L. Jiang Department of Nephrology, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, No 1 Shuaifuyuan, Wangfujing St, Dongchen District, Beijing 100730, China
eventually resulting in EIARF and PRES in patients with RHU. To our knowledge, this is the first report of a homozygous splice-site mutation in the SLC2A9 gene, renal arteriolar chronic lesion, concurrence of RHU and communicating hydrocephalus. Keywords Renal hypouricemia Exercise-induced acute renal failure Posterior reversible encephalopathy syndrome Glucose transporter 9
Introduction Renal hypouricemia (RHU) is an autosomal recessive hereditary disease characterized by impaired renal urate reabsorption and subsequent profound hypouricemia. RHU predisposes affected people to exercise-induced acute renal failure (EIARF), posterior reversible encephalopathy syndrome (PRES) and nephrolithiasis. The common clinical presentations include loin pain, nausea, and vomiting after strenuous exercise [1–3]. Previous studies have revealed two types of RHU: RHU type 1, caused by a loss-offunction mutation of the SLC22A12 gene encoding urate transporter 1 (URAT1, NM_144585.2) which is responsible for control of urate reabsorption at the apical side of proximal tubules; and RHU type 2, caused by a loss-offunction mutation of the SLC2A9 gene encoding glucose transporter 9 (GLUT9). GLUT9 has two variants: the short form (GLUT9S, NM_001001290.1) which is responsible for control of urate absorption at the apical side, and the long form (GLUT9L, NM_020041.2) which is the only major urate efflux transporter at the basolateral side of proximal tubular epithelium. RHU type 2, identified latterly, has a much lower serum uric acid level (near 0 mg/ dl) and higher renal excretion ([100 %) than type 1 [2].
123
J Nephrol
We describe a patient who experienced three episodes of EIARF and one episode of PRES. Cranial magnetic resonance imaging (MRI) showed communicating hydrocephalus. Renal biopsy showed interlobular artery intimal thickening with reduction of lumen. A novel homozygous splice-site mutation––c.1215?1 G[A in GLUT9L (corresponding to c.1128?1 G[A in GLUT9S)––was identified in the SLC2A9 gene.
Dec 16th, SCr and UA dropped to 283 and 74 lmol/l, respectively. On Dec 18th, BP dropped to 150/105 mmHg, and headache, vomiting and nausea all remitted. Therefore, diazepam was withdrawn. On Dec 20th, the patient was discharged. Two weeks after discharge, SCr and BP had returned to normal, the cranial MRI revealed normal occipital lobe and communicating hydrocephalus, but the UA had dropped to 60 lmol/l. Based on the headache, altered mental status, seizure and reversible white matter lesions, the diagnosis of PRES was established.
Case report Second episode First episode On Dec 12th 2000, a patient aged 11 years was admitted to the local hospital with a 3-day history of abdominal pain, vomiting and nausea that had developed immediately after 400-m dash and 1 day of diarrhea. The abdominal pain was dull, persistent and tolerable. Supportive and symptomatic therapy had been administered in the school infirmary, but the symptoms did not improve. Diarrhea occurred 2 days later. The patient had been fit and healthy previously, without remarkable family history or past medical history. On examination, blood pressure (BP) was 127/90 mmHg, pulse 60 beats/min, body temperature 36.8 °C. He was mildly tender in the abdomen without rebound tenderness or guarding. The physical examination was otherwise normal. Urinalysis showed no proteinuria, hematuria or occult blood, and decreased specific gravity (1.010). Ultrasonography of the renal tract was normal. Blood urea nitrogen was 21.34 mmol/l (normal range 2.82–7.12 mmol/l), serum creatinine (SCr) was 456 lmol/l (normal range 44–133 lmol/l), uric acid (UA) was 230 lmol/l (normal range 150–420 lmol/l). He was diagnosed with acute gastroenteritis and acute renal failure. Ceftriaxone and ranitidine were administered intravenously. On Dec 14th, the patient complained of severe headache, and his BP abruptly rose to 195/120 mmHg. Oral nifedipine was administered to lower BP. The headache mildly improved. Cranial computerized tomography (CT) scan showed hydrocephalus. Cranial magnetic resonance imaging (MRI) revealed high signal intensity in the occipital lobe on the T2-weighted images, low signal intensity on the T1weighted images and communicating hydrocephalus. At 5:50 PM on Dec 15th, the patient developed slow response, his eyes were tightly closed, and the head moved involuntarily. The patient was thus transferred to the Neurology Department. At 8:30 PM on Dec 15th, he developed generalized seizure and lost consciousness suddenly, which was resolved within 3 min after 5 mg bolus injection of diazepam followed by 2 mg/h infusion. Lumbar puncture was performed and cerebrospinal pressure was 190 mm H2O. The cerebrospinal fluid test excluded infection. On
123
On May 19th 2005, the patient was admitted to the local hospital again with nausea, vomiting and diarrhea shortly after a 1,000-m race. On examination, his consciousness was clear, BP was 110/80 mmHg, and other vital signs were normal. Urinalysis showed decreased specific gravity (1.010). Investigation showed an increased blood-ureanitrogen (BUN) value of 11.53 mmol/l and increased SCr of 384 lmol/l, but a decreased UA of 41 lmol/l. The cranial MRI showed communicating hydrocephalus. Symptomatic and supportive therapy was administered. The symptoms gradually remitted. One week after admission, the patient was discharged with normal SCr (100 lmol/l) and profound hypouricemia (8 lmol/l). Third episode On Dec 2nd 2008, this patient was admitted to our hospital with a 3-day history of vomiting, bilateral loin pain, fatigue and oliguria which developed immediately after a tug-ofwar contest at school. On physical examination, BP was 142/88 mmHg. He had bilateral renal region percussion pain. Other physical examinations were normal. His urinalysis showed proteinuria 2?, specific gravity (SG) 1.010, but no hematuria or occult blood. The laboratory tests demonstrated increased BUN (10.4 mmol/l) and SCr (380.1 lmol/l), and decreased UA (60 lmol/l). The fraction excretion of urinary uric acid (FEUA) was 139.4 %. On day 11 after onset, after signing the consent form, renal biopsy was performed. Light microcopy showed a nonremarkable glomeruli abnormality, interlobular artery intimal thickening with reduction of lumen (Fig. 1a), tubular epithelium diffuse granular degeneration, and interstitial edema (Fig. 1b). Immunostaining was negative for immunoglobulins and complements. The patient received only symptomatic and supportive therapy. On day 17, Scr had decreased to 88.0 lmol/l, UA to 6 lmol/l. This young patient had recurrent episodes of acute renal failure (ARF) which developed after strenuous exercise. The common causes of ARF, such as severe volume depletion, massive rhabdomyolysis and nephrotoxic drugs,
J Nephrol
had any episode of EIARF. Since RHU predisposes to EIARF, the patient was strictly prohibited from strenuous exercise. EIARF never recurred during 5 years of followup. Gene analysis
Fig. 1 Renal biopsy results. a Light microcopy (HE staining, 9200) shows interlobular artery intima thickening with reduction of lumen (black arrow). b Light microcopy (HE staining, 9200) shows tubular epithelium diffuse granular degeneration
were all excluded. So the diagnosis of EIARF was established. The evidence that he had profound hypouricemia during the period of ARF as well as posterior renal function recovery and significantly increased renal excretion of UA suggested the diagnosis of RHU. Gene analysis of the URAT1 and GLUT9 was carried out in the patient and his family members. Institutional ethics committee approval of genomic analysis and written informed consent of all subjects were obtained. We performed mutational analysis of all coding regions and intron–exon boundaries of the GLUT9 gene and SLC22A12 gene. A novel homozygous splice-site mutation was found in the SLC2A9 gene (Fig. 2), which affected both GLUT9S and GLUT9L. No mutation was detected in the SLC22A12 gene. Eventually, the diagnosis of EIARF due to RHU type 2 was established. UA levels of his mother and younger brother were 139 and 212 lmol/l, respectively. Unfortunately, his father had died of an accident. But no other family member had
Genomic DNA was isolated and purified from peripheral blood of the subjects and used for polymerase chain reaction (PCR) amplification of individual exons of the SLC2A9 gene and SLC22A12 gene. Twenty pairs of oligonucleotide primers were generated to amplify all 23 exons and flanking intronic regions. PCRs were performed in a 50 ll volume containing 100 ng genomic DNA, 0.2 lm primers, 0.2 mm deoxyribonucleotide triphosphate (dNTP), and 5 ll 109 Taq buffer, 2.5 mm MgCl2, 2.5 UTaq enzyme, and 36.3 ll ddH2O. PCR was performed using standard conditions with an initial denaturation step at 94 °C for 3 min, subsequently followed by 35 cycles with denaturation at 94 °C for 30 s, annealing at 55–60 °C for 35 s and elongation at 72 °C for 40–50 s. Sanger direct sequencing was performed on an ABI 3730XL automated DNA sequencer (Applied Biosystems Division, Life Technologies, CA, USA) by Sangon Biotech Shanghai Co., (Shanghai, China). GenBank Accession Numbers NM_020041.2, NM_001001290.1 and NM_144585.2 were used as reference sequences. The numbering of a nucleotide starts at the first adenine of the translation initiation codon. This family carried no mutation in the SLC22A12 gene. The index patient carried one novel homozygous splice-site mutation (c.1215?1 G [ A in GLUT9L, corresponding to c.1128?1 G [ A in GLUT9S). His mother and younger brother carried the same heterozygous splicesite mutation (Fig. 2).
Discussion In this study, we evaluated a Chinese boy who had profound hypouricemia and increased FEUA. This boy experienced three episodes of EIARF and one episode of PRES. Cranial MRI showed communicating hydrocephalus. The renal biopsy displayed interlobular artery intimal thickening with reduction of lumen and acute tubulointerstitial injury. The mutational analysis revealed a homozygous splice-site mutation in the SLC2A9 gene, without mutation in the SLC22A12 gene. To our knowledge, this is the first report of a homozygous splice-site mutation in the SLC2A9 gene, renal arteriolar chronic lesion, concurrence of RHU and communicating hydrocephalus. To date, only 13 mutations including missense, duplication and deletion mutations in the SLC2A9 have been reported [3–7]. At the apical side of proximal renal tubule,
123
J Nephrol Fig. 2 Pedigree of the family and the mutated sequence of GLUT9 polymerase chain reaction (PCR) fragment. a Pedigree of the family. Males and female are indicated by squares and circle; the solid symbol denotes homozygous and half-solid symbols denote heterozygous family members. The arrow indicates the patient. Question mark data unavailable. b–e Novel splice-site mutation in SLC2A9 (c.1215?1 G [ A in GLUT9L, corresponding to c.1128?1 G [ A in GLUT9S). b Wild type; c, d both the patient’s younger brother and his mother carry a heterozygous mutation; e the patient carries a homozygous mutation
A
B Wild type
Exon
Intron
C Mother
Exon
Intron
D Younger brother
Exon
Intron
E Patient
Exon
Intron
GLUT9S as well as URAT1 absorb urate from tubular lumen, but GLUT9L is the sole mediator of the urate efflux at the basolateral side. Therefore, a loss-of-function
123
mutation of URAT1 results in a partial urate absorption defect whereas a loss-of-function mutation of GLUT9 causes a complete absorption defect via blockade of urate
J Nephrol
efflux. RHU type 2 has a much lower serum uric acid level (near 0 mg/dl) and higher renal excretion ([100 %) than type 1. Our patient had profound hypouricemia (serum UA 6 lmol/l) and significantly increased FEUA (139.4 %). Subsequent gene mutation analysis showed a homozygous splice-site mutation in the SLC2A9 gene which affected both GLUT9S and GLUT9L. This mutation was consistent with the profound hypouricemia in this patient. The urate levels of the patient’s mother and younger brother were mildly low and normal, respectively. Gene analysis showed that his mother and younger brother carried a heterozygous mutation in the SLC2A9 gene. Previous studies revealed that a heterozygous nonsense mutation of URAT1 and GLUT9 caused mild hypouricemia or normal urate level probably through haploinsufficiency [2, 3], which might also explain the urate levels of his mother and younger brother. The mechanism of EIARF associated with RHU has not been identified as yet. One well acknowledged explanation is ischemic and reperfusion kidney injury secondary to vasoconstriction of renal vessels mediated by an exerciseinduced increase in oxygen free radicals [8]. UA is recognized to be the most abundant and a potent antioxidant which accounts for half of the antioxidant capacity of human plasma [9]. UA is able to preserve vascular endothelial dilation when oxidative stress occurs [6]. Exercise significantly increases the production of oxygen free radicals. Profound hypouricemia caused by RHU cannot ‘scavenge’ the increased oxygen radicals which eventually result in vasoconstriction. Kaneko et al. [10] first successfully demonstrated increased reactive oxygen species and decreased antioxidant system capability in a patient with RHU type 1 immediately after exercise. This postulation was also supported by CT and electrical capacitance tomography (ECT) imaging results as well as biopsy results of patients with EIARF showing mainly acute tubular necrosis [6]. Delayed (CT) scans after bolus injection of contrast media demonstrated patchy wedge-shaped enhancement [11, 12]. Tc-99m diethylene triamine pentaacetic acid (DTPA) renography showed decreases in both renal blood flow (RBF) and glomerular filtration rate (GFR) at the onset of disease. CT images and Tc-99m DTPA renography improved after symptoms relief. Therefore, it was concluded that vasoconstriction might result in EIARF [13]. Our patient was normotensive before and after the onset of EIARF. However, renal pathology showed interlobular artery intimal thickening accompanied by a reduction of lumen indicative of long-term hypertension. It was not until the third episode of EIARF that RHU was recognized and strenuous exercise prohibited. Before that, this young patient was fond of sport, which may have caused undetected recurrent EIARF. The recurrent episodes of EIARF resulted in repeated renal artery vasoconstriction, and
eventually renal interlobular artery intima thickening. To our knowledge, this is the first report of a renal arteriolar lesion in an RHU patient. PRES is a clinico-radiological entity characterized by headache, altered mental status, visual disturbance, seizure and reversible white matter lesions, predominantly in the posterior region of the cerebral hemispheres on brain CT scan or MRI. It may occur for many reasons, including acute kidney injury (AKI), malignant hypertension, eclampsia and immunosuppression therapy. The first report of EIARF concurrent with PRES occurred in a girl with a compound heterozygous mutation in the GLUT9 gene. The authors speculated that GLUT9 mutation may play a specific role in exercise-induced PRES because this urate transporter is also expressed in the brain [3]. But the next report showed that PRES also occurs in patients with URAT 1 mutation and severe EIARF. An abrupt and severe increase in blood pressure associated with AKI is a well-known risk factor for PRES [14]. Therefore, it was suggested that PRES was a manifestation of severe EIARF associated with RHU because the episode of PRES developed after severe AKI [14]. The speculation mentioned above could not explain the onset of PRES in our patient. The oxidant imbalance due to RHU was systemic; there were some signs suggesting that vessels supplying other organs also were affected. A case of EIARF due to RHU combined with cerebral infarction has been reported. Single photon emission computed tomography (SPECT) showed that the cerebral blood flow of the occipital region was low at the onset, but then recovered. It is indicated that vasoconstriction might affect the brain as well as the kidneys [15, 16]. Electrocardiography (ECG) showed inversed T waves at onset, normalized in parallel with improvement of renal function. As well, no cardiac abnormalities were discovered with either ultrasonic cardiography (UCG) or cardiac loading test. Vasoconstriction might occur in the coronary artery [13]. Therefore, PRES may be caused by cerebrovascular vasoconstriction, sharing the same mechanism as EIARF in RHU patients. MRI revealed communicating hydrocephalus in this patient. There has been no previous report of concurrence of RHU and communicating hydrocephalus, so it may have occurred by chance.
Conclusions We have identified a novel homozygous splice-site mutation in the SLC2A9 gene. Strenuous exercise may induce systemic (including renal and cerebrovascular) vasoconstriction, eventually resulting in EIARF and PRES in patients with RHU. But further study is required to confirm this speculation.
123
J Nephrol Conflict of interest The authors did not receive any pharmaceutical and industry support.
References 1. Tasic V, Hynes AM, Kitamura K et al (2011) Clinical and functional characterization of URAT1 variants. PLoS One 6(12):e28641 2. Dinour D, Gray NK, Ganon L et al (2012) Two novel homozygous SLC2A9 mutations cause renal hypouricemia type 2. Nephrol Dial Transpl 27(3):1035–1041 3. Shima Y, Nozu K, Nozu Y et al (2011) Recurrent EIARF and PRES with severe renal hypouricemia by compound heterozygous SLC2A9 mutation. Pediatrics 127(6):e1621–e1625 4. Anzai N, Ichida K, Jutabha P et al (2008) Plasma urate level is directly regulated by a voltage-driven urate efflux transporter URAT1 (SLC2A9) in humans. J Biol Chem 283(40):26834– 26838 5. Matsuo H, Chiba T, Nagamori S et al (2008) Mutations in glucose transporter 9 gene SLC2A9 cause renal hypouricemia. Am J Hum Genet 83(6):744–751 6. Dinour D, Gray NK, Campbell S et al (2010) Homozygous SLC2A9 mutations cause severe renal hypouricemia. J Am Soc Nephrol 21(1):64–72 7. Li Z, Ding H, Chen C et al (2013) Novel URAT1 mutations caused acute renal failure after exercise in two Chinese families with renal hypouricemia. Gene 512(1):97–101
123
8. Sperling O (2006) Hereditary renal hypouricemia. Mol Genet Metab 89(1–2):14–18 9. So A, Thorens B (2010) Uric acid transport and disease. J Clin Invest 120(6):1791–1799 10. Kaneko K, Taniguchi N, Tanabe Y et al (2009) Oxidative imbalance in idiopathic renal hypouricemia. Pediatr Nephrol 24(4):869–871 11. Ishikawa I, Nakagawa M, Hayama S et al (2005) Acute renal failure with severe loin pain and patchy renal ischaemia after anaerobic exercise (ALPE) (exercise-induced acute renal failure) in a father and child with URAT1 mutations beyond the W258X mutation. Nephrol Dial Transpl 20(5):1015 12. Ishikawa I (2002) Acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise in patients with or without renal hypouricemia. Nephron 91(4):559–570 13. Nishida H, Kaida H, Ishibashi M et al (2005) Evaluation of exercise-induced acute renal failure in renal hypouricemia using Tc-99m DTPA renography. Ann Nucl Med 19(4):325–329 14. Fujinaga S, Ito A, Nakagawa M et al (2013) Posterior reversible encephalopathy syndrome with exercise-induced acute kidney injury in renal hypouricemia type 1. Eur J Pediatr 172(11): 1557–1560 15. Ueda O, Oka T, Kyan H (1997) A case of renal hypouricemia with exercise-induced acute renal failure and cerebral infarction. J Jpn Pediatr Soc 101(5):1620–1625 16. Watanabe T, Abe T, Oda Y (2000) Exercise-induced acute renal failure in a patient with renal hypouricemia. Pediatr Nephrol 14(8–9):851–852
CASE REPORT
A novel homozygous GLUT9 mutation cause recurrent exerciseinduced acute renal failure and posterior reversible encephalopathy syndrome Li-jun Mou • Lan-ping Jiang • Ying Hu
Received: 22 October 2013 / Accepted: 19 February 2014 Ó Italian Society of Nephrology 2014
Abstract Renal hypouricemia (RHU) is an autosomal recessive hereditary disease characterized by impaired renal urate reabsorption and subsequent profound hypouricemia. There are two types of RHU, type 1 and type 2, caused by the loss-of-function mutation of SLC22A12 and SLC2A9 genes, respectively. RHU predisposes affected people to exercise-induced acute renal failure (EIARF), posterior reversible encephalopathy syndrome (PRES) and nephrolithiasis. A Chinese patient had experienced three episodes of EIARF and one episode of PRES. The investigations showed profound hypouricemia and significantly increased renal excretion of UA. Cranial magnetic resonance imaging showed communicating hydrocephalus. Renal biopsy displayed interlobular artery intimal thickening with reduction of lumen and acute tubulointerstitial injury. The mutational analysis revealed a homozygous splice-site mutation in the SLC2A9 gene encoding glucose transporter 9. The patient was diagnosed as RHU type 2 caused by a loss-of-function mutation of the SLC2A9 gene. Consequently, he was strictly prohibited from strenuous exercise. During the 5-year follow-up, EIARF and PRES never recurred. Strenuous exercise may induce systemic (including renal and cerebrovascular) vasoconstriction
L. Mou Y. Hu (&) Department of Nephrology, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Jiefang Rd 88, Hangzhou 31009, China e-mail: [email protected] L. Jiang Department of Nephrology, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, No 1 Shuaifuyuan, Wangfujing St, Dongchen District, Beijing 100730, China
eventually resulting in EIARF and PRES in patients with RHU. To our knowledge, this is the first report of a homozygous splice-site mutation in the SLC2A9 gene, renal arteriolar chronic lesion, concurrence of RHU and communicating hydrocephalus. Keywords Renal hypouricemia Exercise-induced acute renal failure Posterior reversible encephalopathy syndrome Glucose transporter 9
Introduction Renal hypouricemia (RHU) is an autosomal recessive hereditary disease characterized by impaired renal urate reabsorption and subsequent profound hypouricemia. RHU predisposes affected people to exercise-induced acute renal failure (EIARF), posterior reversible encephalopathy syndrome (PRES) and nephrolithiasis. The common clinical presentations include loin pain, nausea, and vomiting after strenuous exercise [1–3]. Previous studies have revealed two types of RHU: RHU type 1, caused by a loss-offunction mutation of the SLC22A12 gene encoding urate transporter 1 (URAT1, NM_144585.2) which is responsible for control of urate reabsorption at the apical side of proximal tubules; and RHU type 2, caused by a loss-offunction mutation of the SLC2A9 gene encoding glucose transporter 9 (GLUT9). GLUT9 has two variants: the short form (GLUT9S, NM_001001290.1) which is responsible for control of urate absorption at the apical side, and the long form (GLUT9L, NM_020041.2) which is the only major urate efflux transporter at the basolateral side of proximal tubular epithelium. RHU type 2, identified latterly, has a much lower serum uric acid level (near 0 mg/ dl) and higher renal excretion ([100 %) than type 1 [2].
123
J Nephrol
We describe a patient who experienced three episodes of EIARF and one episode of PRES. Cranial magnetic resonance imaging (MRI) showed communicating hydrocephalus. Renal biopsy showed interlobular artery intimal thickening with reduction of lumen. A novel homozygous splice-site mutation––c.1215?1 G[A in GLUT9L (corresponding to c.1128?1 G[A in GLUT9S)––was identified in the SLC2A9 gene.
Dec 16th, SCr and UA dropped to 283 and 74 lmol/l, respectively. On Dec 18th, BP dropped to 150/105 mmHg, and headache, vomiting and nausea all remitted. Therefore, diazepam was withdrawn. On Dec 20th, the patient was discharged. Two weeks after discharge, SCr and BP had returned to normal, the cranial MRI revealed normal occipital lobe and communicating hydrocephalus, but the UA had dropped to 60 lmol/l. Based on the headache, altered mental status, seizure and reversible white matter lesions, the diagnosis of PRES was established.
Case report Second episode First episode On Dec 12th 2000, a patient aged 11 years was admitted to the local hospital with a 3-day history of abdominal pain, vomiting and nausea that had developed immediately after 400-m dash and 1 day of diarrhea. The abdominal pain was dull, persistent and tolerable. Supportive and symptomatic therapy had been administered in the school infirmary, but the symptoms did not improve. Diarrhea occurred 2 days later. The patient had been fit and healthy previously, without remarkable family history or past medical history. On examination, blood pressure (BP) was 127/90 mmHg, pulse 60 beats/min, body temperature 36.8 °C. He was mildly tender in the abdomen without rebound tenderness or guarding. The physical examination was otherwise normal. Urinalysis showed no proteinuria, hematuria or occult blood, and decreased specific gravity (1.010). Ultrasonography of the renal tract was normal. Blood urea nitrogen was 21.34 mmol/l (normal range 2.82–7.12 mmol/l), serum creatinine (SCr) was 456 lmol/l (normal range 44–133 lmol/l), uric acid (UA) was 230 lmol/l (normal range 150–420 lmol/l). He was diagnosed with acute gastroenteritis and acute renal failure. Ceftriaxone and ranitidine were administered intravenously. On Dec 14th, the patient complained of severe headache, and his BP abruptly rose to 195/120 mmHg. Oral nifedipine was administered to lower BP. The headache mildly improved. Cranial computerized tomography (CT) scan showed hydrocephalus. Cranial magnetic resonance imaging (MRI) revealed high signal intensity in the occipital lobe on the T2-weighted images, low signal intensity on the T1weighted images and communicating hydrocephalus. At 5:50 PM on Dec 15th, the patient developed slow response, his eyes were tightly closed, and the head moved involuntarily. The patient was thus transferred to the Neurology Department. At 8:30 PM on Dec 15th, he developed generalized seizure and lost consciousness suddenly, which was resolved within 3 min after 5 mg bolus injection of diazepam followed by 2 mg/h infusion. Lumbar puncture was performed and cerebrospinal pressure was 190 mm H2O. The cerebrospinal fluid test excluded infection. On
123
On May 19th 2005, the patient was admitted to the local hospital again with nausea, vomiting and diarrhea shortly after a 1,000-m race. On examination, his consciousness was clear, BP was 110/80 mmHg, and other vital signs were normal. Urinalysis showed decreased specific gravity (1.010). Investigation showed an increased blood-ureanitrogen (BUN) value of 11.53 mmol/l and increased SCr of 384 lmol/l, but a decreased UA of 41 lmol/l. The cranial MRI showed communicating hydrocephalus. Symptomatic and supportive therapy was administered. The symptoms gradually remitted. One week after admission, the patient was discharged with normal SCr (100 lmol/l) and profound hypouricemia (8 lmol/l). Third episode On Dec 2nd 2008, this patient was admitted to our hospital with a 3-day history of vomiting, bilateral loin pain, fatigue and oliguria which developed immediately after a tug-ofwar contest at school. On physical examination, BP was 142/88 mmHg. He had bilateral renal region percussion pain. Other physical examinations were normal. His urinalysis showed proteinuria 2?, specific gravity (SG) 1.010, but no hematuria or occult blood. The laboratory tests demonstrated increased BUN (10.4 mmol/l) and SCr (380.1 lmol/l), and decreased UA (60 lmol/l). The fraction excretion of urinary uric acid (FEUA) was 139.4 %. On day 11 after onset, after signing the consent form, renal biopsy was performed. Light microcopy showed a nonremarkable glomeruli abnormality, interlobular artery intimal thickening with reduction of lumen (Fig. 1a), tubular epithelium diffuse granular degeneration, and interstitial edema (Fig. 1b). Immunostaining was negative for immunoglobulins and complements. The patient received only symptomatic and supportive therapy. On day 17, Scr had decreased to 88.0 lmol/l, UA to 6 lmol/l. This young patient had recurrent episodes of acute renal failure (ARF) which developed after strenuous exercise. The common causes of ARF, such as severe volume depletion, massive rhabdomyolysis and nephrotoxic drugs,
J Nephrol
had any episode of EIARF. Since RHU predisposes to EIARF, the patient was strictly prohibited from strenuous exercise. EIARF never recurred during 5 years of followup. Gene analysis
Fig. 1 Renal biopsy results. a Light microcopy (HE staining, 9200) shows interlobular artery intima thickening with reduction of lumen (black arrow). b Light microcopy (HE staining, 9200) shows tubular epithelium diffuse granular degeneration
were all excluded. So the diagnosis of EIARF was established. The evidence that he had profound hypouricemia during the period of ARF as well as posterior renal function recovery and significantly increased renal excretion of UA suggested the diagnosis of RHU. Gene analysis of the URAT1 and GLUT9 was carried out in the patient and his family members. Institutional ethics committee approval of genomic analysis and written informed consent of all subjects were obtained. We performed mutational analysis of all coding regions and intron–exon boundaries of the GLUT9 gene and SLC22A12 gene. A novel homozygous splice-site mutation was found in the SLC2A9 gene (Fig. 2), which affected both GLUT9S and GLUT9L. No mutation was detected in the SLC22A12 gene. Eventually, the diagnosis of EIARF due to RHU type 2 was established. UA levels of his mother and younger brother were 139 and 212 lmol/l, respectively. Unfortunately, his father had died of an accident. But no other family member had
Genomic DNA was isolated and purified from peripheral blood of the subjects and used for polymerase chain reaction (PCR) amplification of individual exons of the SLC2A9 gene and SLC22A12 gene. Twenty pairs of oligonucleotide primers were generated to amplify all 23 exons and flanking intronic regions. PCRs were performed in a 50 ll volume containing 100 ng genomic DNA, 0.2 lm primers, 0.2 mm deoxyribonucleotide triphosphate (dNTP), and 5 ll 109 Taq buffer, 2.5 mm MgCl2, 2.5 UTaq enzyme, and 36.3 ll ddH2O. PCR was performed using standard conditions with an initial denaturation step at 94 °C for 3 min, subsequently followed by 35 cycles with denaturation at 94 °C for 30 s, annealing at 55–60 °C for 35 s and elongation at 72 °C for 40–50 s. Sanger direct sequencing was performed on an ABI 3730XL automated DNA sequencer (Applied Biosystems Division, Life Technologies, CA, USA) by Sangon Biotech Shanghai Co., (Shanghai, China). GenBank Accession Numbers NM_020041.2, NM_001001290.1 and NM_144585.2 were used as reference sequences. The numbering of a nucleotide starts at the first adenine of the translation initiation codon. This family carried no mutation in the SLC22A12 gene. The index patient carried one novel homozygous splice-site mutation (c.1215?1 G [ A in GLUT9L, corresponding to c.1128?1 G [ A in GLUT9S). His mother and younger brother carried the same heterozygous splicesite mutation (Fig. 2).
Discussion In this study, we evaluated a Chinese boy who had profound hypouricemia and increased FEUA. This boy experienced three episodes of EIARF and one episode of PRES. Cranial MRI showed communicating hydrocephalus. The renal biopsy displayed interlobular artery intimal thickening with reduction of lumen and acute tubulointerstitial injury. The mutational analysis revealed a homozygous splice-site mutation in the SLC2A9 gene, without mutation in the SLC22A12 gene. To our knowledge, this is the first report of a homozygous splice-site mutation in the SLC2A9 gene, renal arteriolar chronic lesion, concurrence of RHU and communicating hydrocephalus. To date, only 13 mutations including missense, duplication and deletion mutations in the SLC2A9 have been reported [3–7]. At the apical side of proximal renal tubule,
123
J Nephrol Fig. 2 Pedigree of the family and the mutated sequence of GLUT9 polymerase chain reaction (PCR) fragment. a Pedigree of the family. Males and female are indicated by squares and circle; the solid symbol denotes homozygous and half-solid symbols denote heterozygous family members. The arrow indicates the patient. Question mark data unavailable. b–e Novel splice-site mutation in SLC2A9 (c.1215?1 G [ A in GLUT9L, corresponding to c.1128?1 G [ A in GLUT9S). b Wild type; c, d both the patient’s younger brother and his mother carry a heterozygous mutation; e the patient carries a homozygous mutation
A
B Wild type
Exon
Intron
C Mother
Exon
Intron
D Younger brother
Exon
Intron
E Patient
Exon
Intron
GLUT9S as well as URAT1 absorb urate from tubular lumen, but GLUT9L is the sole mediator of the urate efflux at the basolateral side. Therefore, a loss-of-function
123
mutation of URAT1 results in a partial urate absorption defect whereas a loss-of-function mutation of GLUT9 causes a complete absorption defect via blockade of urate
J Nephrol
efflux. RHU type 2 has a much lower serum uric acid level (near 0 mg/dl) and higher renal excretion ([100 %) than type 1. Our patient had profound hypouricemia (serum UA 6 lmol/l) and significantly increased FEUA (139.4 %). Subsequent gene mutation analysis showed a homozygous splice-site mutation in the SLC2A9 gene which affected both GLUT9S and GLUT9L. This mutation was consistent with the profound hypouricemia in this patient. The urate levels of the patient’s mother and younger brother were mildly low and normal, respectively. Gene analysis showed that his mother and younger brother carried a heterozygous mutation in the SLC2A9 gene. Previous studies revealed that a heterozygous nonsense mutation of URAT1 and GLUT9 caused mild hypouricemia or normal urate level probably through haploinsufficiency [2, 3], which might also explain the urate levels of his mother and younger brother. The mechanism of EIARF associated with RHU has not been identified as yet. One well acknowledged explanation is ischemic and reperfusion kidney injury secondary to vasoconstriction of renal vessels mediated by an exerciseinduced increase in oxygen free radicals [8]. UA is recognized to be the most abundant and a potent antioxidant which accounts for half of the antioxidant capacity of human plasma [9]. UA is able to preserve vascular endothelial dilation when oxidative stress occurs [6]. Exercise significantly increases the production of oxygen free radicals. Profound hypouricemia caused by RHU cannot ‘scavenge’ the increased oxygen radicals which eventually result in vasoconstriction. Kaneko et al. [10] first successfully demonstrated increased reactive oxygen species and decreased antioxidant system capability in a patient with RHU type 1 immediately after exercise. This postulation was also supported by CT and electrical capacitance tomography (ECT) imaging results as well as biopsy results of patients with EIARF showing mainly acute tubular necrosis [6]. Delayed (CT) scans after bolus injection of contrast media demonstrated patchy wedge-shaped enhancement [11, 12]. Tc-99m diethylene triamine pentaacetic acid (DTPA) renography showed decreases in both renal blood flow (RBF) and glomerular filtration rate (GFR) at the onset of disease. CT images and Tc-99m DTPA renography improved after symptoms relief. Therefore, it was concluded that vasoconstriction might result in EIARF [13]. Our patient was normotensive before and after the onset of EIARF. However, renal pathology showed interlobular artery intimal thickening accompanied by a reduction of lumen indicative of long-term hypertension. It was not until the third episode of EIARF that RHU was recognized and strenuous exercise prohibited. Before that, this young patient was fond of sport, which may have caused undetected recurrent EIARF. The recurrent episodes of EIARF resulted in repeated renal artery vasoconstriction, and
eventually renal interlobular artery intima thickening. To our knowledge, this is the first report of a renal arteriolar lesion in an RHU patient. PRES is a clinico-radiological entity characterized by headache, altered mental status, visual disturbance, seizure and reversible white matter lesions, predominantly in the posterior region of the cerebral hemispheres on brain CT scan or MRI. It may occur for many reasons, including acute kidney injury (AKI), malignant hypertension, eclampsia and immunosuppression therapy. The first report of EIARF concurrent with PRES occurred in a girl with a compound heterozygous mutation in the GLUT9 gene. The authors speculated that GLUT9 mutation may play a specific role in exercise-induced PRES because this urate transporter is also expressed in the brain [3]. But the next report showed that PRES also occurs in patients with URAT 1 mutation and severe EIARF. An abrupt and severe increase in blood pressure associated with AKI is a well-known risk factor for PRES [14]. Therefore, it was suggested that PRES was a manifestation of severe EIARF associated with RHU because the episode of PRES developed after severe AKI [14]. The speculation mentioned above could not explain the onset of PRES in our patient. The oxidant imbalance due to RHU was systemic; there were some signs suggesting that vessels supplying other organs also were affected. A case of EIARF due to RHU combined with cerebral infarction has been reported. Single photon emission computed tomography (SPECT) showed that the cerebral blood flow of the occipital region was low at the onset, but then recovered. It is indicated that vasoconstriction might affect the brain as well as the kidneys [15, 16]. Electrocardiography (ECG) showed inversed T waves at onset, normalized in parallel with improvement of renal function. As well, no cardiac abnormalities were discovered with either ultrasonic cardiography (UCG) or cardiac loading test. Vasoconstriction might occur in the coronary artery [13]. Therefore, PRES may be caused by cerebrovascular vasoconstriction, sharing the same mechanism as EIARF in RHU patients. MRI revealed communicating hydrocephalus in this patient. There has been no previous report of concurrence of RHU and communicating hydrocephalus, so it may have occurred by chance.
Conclusions We have identified a novel homozygous splice-site mutation in the SLC2A9 gene. Strenuous exercise may induce systemic (including renal and cerebrovascular) vasoconstriction, eventually resulting in EIARF and PRES in patients with RHU. But further study is required to confirm this speculation.
123
J Nephrol Conflict of interest The authors did not receive any pharmaceutical and industry support.
References 1. Tasic V, Hynes AM, Kitamura K et al (2011) Clinical and functional characterization of URAT1 variants. PLoS One 6(12):e28641 2. Dinour D, Gray NK, Ganon L et al (2012) Two novel homozygous SLC2A9 mutations cause renal hypouricemia type 2. Nephrol Dial Transpl 27(3):1035–1041 3. Shima Y, Nozu K, Nozu Y et al (2011) Recurrent EIARF and PRES with severe renal hypouricemia by compound heterozygous SLC2A9 mutation. Pediatrics 127(6):e1621–e1625 4. Anzai N, Ichida K, Jutabha P et al (2008) Plasma urate level is directly regulated by a voltage-driven urate efflux transporter URAT1 (SLC2A9) in humans. J Biol Chem 283(40):26834– 26838 5. Matsuo H, Chiba T, Nagamori S et al (2008) Mutations in glucose transporter 9 gene SLC2A9 cause renal hypouricemia. Am J Hum Genet 83(6):744–751 6. Dinour D, Gray NK, Campbell S et al (2010) Homozygous SLC2A9 mutations cause severe renal hypouricemia. J Am Soc Nephrol 21(1):64–72 7. Li Z, Ding H, Chen C et al (2013) Novel URAT1 mutations caused acute renal failure after exercise in two Chinese families with renal hypouricemia. Gene 512(1):97–101
123
8. Sperling O (2006) Hereditary renal hypouricemia. Mol Genet Metab 89(1–2):14–18 9. So A, Thorens B (2010) Uric acid transport and disease. J Clin Invest 120(6):1791–1799 10. Kaneko K, Taniguchi N, Tanabe Y et al (2009) Oxidative imbalance in idiopathic renal hypouricemia. Pediatr Nephrol 24(4):869–871 11. Ishikawa I, Nakagawa M, Hayama S et al (2005) Acute renal failure with severe loin pain and patchy renal ischaemia after anaerobic exercise (ALPE) (exercise-induced acute renal failure) in a father and child with URAT1 mutations beyond the W258X mutation. Nephrol Dial Transpl 20(5):1015 12. Ishikawa I (2002) Acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise in patients with or without renal hypouricemia. Nephron 91(4):559–570 13. Nishida H, Kaida H, Ishibashi M et al (2005) Evaluation of exercise-induced acute renal failure in renal hypouricemia using Tc-99m DTPA renography. Ann Nucl Med 19(4):325–329 14. Fujinaga S, Ito A, Nakagawa M et al (2013) Posterior reversible encephalopathy syndrome with exercise-induced acute kidney injury in renal hypouricemia type 1. Eur J Pediatr 172(11): 1557–1560 15. Ueda O, Oka T, Kyan H (1997) A case of renal hypouricemia with exercise-induced acute renal failure and cerebral infarction. J Jpn Pediatr Soc 101(5):1620–1625 16. Watanabe T, Abe T, Oda Y (2000) Exercise-induced acute renal failure in a patient with renal hypouricemia. Pediatr Nephrol 14(8–9):851–852
