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Pediatrics International (2014) 56, e41–e44
doi: 10.1111/ped.12395
Patient Report
Novel mutation in the TMPRSS6 gene with iron-refractory iron deficiency anemia Koya Kodama, Atsuko Noguchi, Hiroyuki Adachi, Miwa Hebiguchi, Michihiro Yano and Tsutomu Takahashi Department of Pediatrics, Akita University Graduate School of Medicine, Akita, Japan Abstract
Iron-refractory iron deficiency anemia (IRIDA) is a rare autosomal recessive disease characterized by congenital hypochromic microcytic anemia, low transferrin saturation, low serum iron, normal–high serum ferritin, and increased hepcidin. This disease is caused by loss-of-function mutations in TMPRSS6 that lead to high hepcidin and result in severe anemia. We report our experience with an 11-year-old Japanese girl with hypochromic microcytic anemia, low serum iron, and high serum ferritin, with anemia that was refractory to the oral iron that was prescribed frequently from early childhood. Presence of high hepcidin suggested a diagnosis of IRIDA, which was eventually confirmed by identification of a novel homozygous mutation, p.Pro354Leu, in the TMPRSS6 gene. This case suggests that serum hepcidin should be routinely measured for differential diagnosis when patients with IDA are unresponsive to oral iron or have unusual clinical features.
Key words hepcidin, iron refractory iron deficiency anemia, TMPRSS6.
Iron-refractory iron deficiency anemia (IRIDA) is a rare autosomal recessive disease characterized by congenital hypochromic microcytic anemia, low transferrin saturation, low serum iron, normal–high serum ferritin, and increased hepcidin.1 This disease is caused by mutations in the TMPRSS6 gene, which encodes matriptase-2 (MT2), a member of the type II transmembrane serine protease family that is mainly expressed in the liver.1 TMPRSS6 plays a role in iron metabolism through regulation of the expression of hepcidin, the key protein in iron homeostasis.2 Hepcidin binds to ferroportin, the channel for cellular iron efflux, and induces its internalization and degradation. In patients with IRIDA, high hepcidin, which is caused by defective negative control by TMPRSS6, prevent duodenal absorption and recycling of heme iron by macrophages, resulting in severe anemia. To date, more than 30 TMPRSS6 gene mutations have been identified in patients with IRIDA.3 Correlation between phenotype and genotype has not yet been established in this disease. In this report, we present a case of IRIDA in a Japanese patient caused by a novel homozygous mutation of the TMPRSS6 gene.
Case report An 11-year-old Japanese girl visited hospital because of fatigue and faintness after heavy exercise. On physical examination there were no obvious signs indicating any specific disease, but
Correspondence: Atsuko Noguchi, MD PhD, Department of Pediatrics, Akita Graduate School of Medicine, Akita-shi, Akita 010-8543, Japan. Email: [email protected] Received 5 September 2013; revised 28 February 2014; accepted 24 March 2014.
© 2014 Japan Pediatric Society
laboratory findings showed severe IDA. Laboratory data (Table 1) indicated hypochromic hypovolemic anemia with low serum iron and ferritin, and low saturated transferrin. Clinically, the patient had no fever, appetite had been good and the patient had a balanced diet. There was no occult blood in the stool, and serum Helicobacter pylori antibody was negative. Blood test and urinalysis data indicated no inflammation. Imaging was also normal, therefore various etiologies of anemia, such as intestinal bleeding and chronic inflammation (autoimmune disease, malignant tumor, chronic kidney disease) including H. pylori, were ruled out.
Table 1 Laboratory data Parameter WBC (×103/μL) RBC (×104/μL) Hb (g/dL) Hct (%) MCV (fL) MCH (pg) MCHC (%) Platelets (×103/μL) Reticulocyte (‰) Iron (μg/dL) TIBC (μg/dL) UIBC (μg/dL) Ferritin (ng/mL) Transferrin (mg/dL)
Patient 4.3 506 8.6 29.5 58.3 17 29.2 389 8.8 9 371 362 21.2 243
Reference range 4.0–9.0 380–480 12.0–15.2 34.0–42.0 78.0–110.0 28.0–35.0 31.0–36.0 117–329 7.0–25.0 55–178 245–430 120–340 12.0–60.0 190–320
Hb, hemoglobin; Hct, hematocrit; MCHC, mean corpuscular hemoglobin concentration; MCV, mean corpuscular volume; RBC, red blood cell; TIBC, total iron binding capacity; UIBC, unsaturated iron binding capacity; WBC, white blood cell.
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Before the patient visited hospital, ferrous sulfate was given orally, but IDA was refractory to treatment. Therefore, we diagnosed the patient with IRIDA on the basis of the clinical course and findings. To confirm the diagnosis, we measured serum hepcidin and performed a mutational analysis of TMPRSS6. This study was approved by the ethics committee of Akita University Graduate School of Medicine, and written informed consent was obtained from the patient and her guardian. Serum hepcidin, which was measured using enzyme-linked immunoassay (ELISA) after parenteral iron treatment, was found to be 31.5 ng/mL, (normal range, 7.8 ± 7.0 ng/mL), despite low hemoglobin (Hb; 8.6 g/dL) and low serum iron (5 ng/mL). Mutational analysis of TMPRSS6 identified a novel mutation, c.1175C>T, leading to a replacement of a proline by a leucine at position 354, designated as p.Pro354Leu (Fig. 1). The patient was homozygous whereas her mother was heterozygous for the mutation. The father’s DNA was not available. Given that the patient was diagnosed with IRIDA, we prescribed monthly i.v. iron sucrose (40 mg). After the fourth consecutive treatment, serum ferritin rose from 21.2 to 37.8 ng/mL and Hb increased to 9.3 g/dL.
Discussion We here report a case of IRIDA in a Japanese patient that was caused by a novel homozygous mutation of TMPRSS6 p.Pro354Leu (Fig. 2b). MT2, the protein encoded by TMPRSS6, is composed of a small cytoplasmic domain, a transmembrane domain, a stem region consisting of a sea urchin sperm protein enterokinase agrin (SEA) domain, two C1s/C1r, urchin embryonic growth factor and bone morphogenetic protein-1 (CUB) domains, three low-density lipoprotein receptor class A (LDIRA) domains, and a carboxy-terminal serine protease (SP) domain, listed in order from the N- to the C-terminus.15 MT2 is synthesized as a zymogen that is autoactivated through cleavage by its own trypsin-like serine protease activity. Autoactivation of the zymogen is characterized by cleavage after Arg 576 within a highly conserved Arg-Ile-Val-Gly-Gly (RIVGG) motif located at the junction between the SP domain and the stem. The active
protease is released from the cell membrane into the extracellular medium after a series of steps including multimerization, transactivation, and proteolytic cleavage within the stem. p.Pro354Leu is located at the middle of the second CUB domain of the TMPRSS6 protein. We randomly selected 50 healthy controls with informed consent from Akita Prefectures to determine the minor allele frequency for the identified candidate variants. The haplotype carrying this variant was not observed in 50 controls, nor in any of the publically available databases we examined; we are therefore tempted to speculate that the combination of this variant led to IRIDA in the present patient. To predict the functional effects of the mutation, we performed in silico analysis using PolyPhen-2 (http:// genetics.bwh.harvard.edu/pph2/). This online tool can be used to predict the possible impact of an amino acid substitution on the structure and function of a human protein. The mutation was classified as being “probably damaging”. In addition to PolyPhen-2 analysis, we investigated protein sequence conservation among vertebrates. Pro354 is a highly conserved residue in the CUB domain of TMPRSS6 across different species (Fig. 2a). This further indicated that p.Pro354Leu was a novel mutation. To date, five other mutations responsible for IRIDA have been identified in the second CUB domain of TMPRSS6: p.Y355X,1 p.H369N,16 p.Y393X,8 p.Y418C,15 and p.G442R.1 Mutagenesis and expression studies of p.Y418C showed that although it was characterized by a reduction in autoactivating cleavage, it retained some of its transcriptional repression activity. The precise functional role of the CUB2 domain is yet to be elucidated, but mutations in this domain might cause functional defects in the TMPRSS6 zymogen. The two reports describe successful oral iron therapy in families with IRIDA caused by TMPRSS6 gene mutations. One report described a patient homozygous for the IVS6+1G>C mutation of TMPRSS6, who had responsiveness to oral iron supplemented with ascorbic acid.18 The other report described two siblings with IRIDA who were responsive to continued oral iron therapy without any supplementation.3 These studies indicate the clinical diversity of IRIDA and suggest the possibility of treatment with
Fig. 1 TMPRSS6 genotype in a Japanese patient with iron-refractory iron deficiency anemia. (a) Pedigree of the family. Eu, examination uninformative; P, proband. (b,c) Sequences of exon 9 of the TMPRSS6 gene in (b) the patient and (c) the mother. Arrows: (c) heterozygous nucleotide substitution in the mother; (b) homozygous nucleotide substitution in the patient. The substitution leads to the replacement of a proline by a leucine at position 354 of TMPRSS6, designated as p.Pro354Leu. © 2014 Japan Pediatric Society
Novel TMPRSS6 mutation in a Japanese girl
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VFQACEVNLTLDNRLDSQGVLSTPYFPSYYSPQTHCSWHLTVPSLDYGLALWFDAYAL VFQACEVNLXLGRWVHQPG--HTPWATWPAPPS-------QVPSLDYGLALWFDAYAL AFQDCQVNLTLEGRLDTQGFLRTPYYPSYYSPSTHCSWHLTVPSLDYGLALWFDAYAL TIQACEVNLTLEGRLEPQGVLSTPYFPSYYSPSTHCSWHLTVPSLDYGLALWFDAYAL PLKACGVNITLREGLELQGKISTPHYPSYYSPNTQCTWHMSVPSLDYGVTLWFDAYAL PDQVCSLSVVLEQTLAVQGVLRTPFYPSYYPPDTNCSWTFTVPSVDYGLTLAFEGYEL
A736V11 P765A15 R774C1
L674F10 P686fs17
K636fs1
G603R9 A605fs1
R599X8
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ATG
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C510S6 D521N1 E522K3
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Y355X1 H369N16 Y393X8 Y418C15 G442R1,3 E461fs1
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Delg29139_3019213
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Q229fs6 L235P15 W247fs6 K253E7 R271Q6 S304L6,13
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Fig. 2 (a) Matriptase-2 CUB domain sequences from different species were aligned using Evola version 7.5 (http://www.h-invitational.jp/ evola_main/annotation.cgi?hit=HIT000083936).4 Box, residues corresponding to human proline. Sequences were obtained from the following GenBank entries: human, AY055384; chimpanzee, XR_024662; mouse, AY240929; cow, XM_001255604; chicken, XM_416281; zebrafish, XM_001920132. (b) Matriptase-2 gene/protein structures and locations of IRIDA mutations. Upper panel, encoded protein. Arrows, currently identified iron-refractory iron deficiency anemia (IRIDA) patient mutations on the matriptase-2 protein, corresponding to their genomic locations.5–14 C, C-terminal; CUB, C1s/C1r, urchin embryonic growth factor, and bone morphogenetic protein-1 domain; L, low-densitylipoprotein receptor, class A domain; N, N-terminal domain; SEA, sea urchin sperm protein enterokinase agrin domain; TM, transmembranespanning region. Lower panel, genomic structure of matriptase-2. Black box, coding region; white box, non-coding region.
oral iron therapy. Anemia has a potent influence on quality of life. Given that IRIDA is a rare disease, patients may often fail to be accurately diagnosed. Recently, hepcidin has been recognized as an acute-phase reactant that plays a critical role in inflammation and iron homeostasis.19,20 Serum hepcidin may be a biomarker for several disorders, including infection, inflammatory disease, and even obesity. Therefore, its measurement has become common.21,22 Serum hepcidin should be routinely measured for differential diagnosis when patients with IDA are unresponsive to oral iron therapy or have unusual clinical features.
Acknowledgments The authors thank Harumi Sugawara and Maiko Ito at Akita University School of Medicine for their technical assistance.
References 1 Finberg KE, Heeney MM, Campagna DR et al. Mutations in TMPRSS6 cause iron-refractory iron deficiency anemia (IRIDA). Nat. Genet. 2008; 40: 569–71. 2 Du X, She E, Gelbart T et al. The serine protease TMPRSS6 is required to sense iron deficiency. Science 2008; 320: 1088– 92. 3 Khuong-Quang DA, Schwartzentruber J, Westerman M et al. Iron refractory iron deficiency anemia: Presentation with hyperferritinemia and response to oral iron therapy. Pediatrics 2013; 131: e620–25. 4 Matsuya A, Sakate R, Kawahara Y et al. Evola: Ortholog database of all human genes in H-InvDB with manual curation of phylogenetic trees. Nucleic Acids Res. 2008; 36: D787– 92. 5 Altamura S, D’Alessio F, Selle B, Muckenthaler MU. A novel TMPRSS6 mutation that prevents protease auto-activation causes IRIDA. Biochem. J. 2010; 431: 363–71.
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6 De Falco L, Totaro F, Nai A et al. Novel TMPRSS6 mutations associated with iron-refractory iron deficiency anemia (IRIDA). Hum. Mutat. 2010; 31: E1390–405. 7 Sato T, Iyama S, Murase K et al. Novel missense mutation in the TMPRSS6 gene in a Japanese female with iron-refractory iron deficiency anemia. Int. J. Hematol. 2011; 94: 101–3. 8 Guillem F, Lawson S, Kannengiesser C, Westerman M, Beaumont C, Grandchamp B. Two nonsense mutations in the TMPRSS6 gene in a patient with microcytic anemia and iron deficiency. Blood 2008; 112: 2089–91. 9 Choi HS, Yang HR, Song SH, Seo JY, Lee KO, Kim HJ. A novel mutation Gly603Arg of TMPRSS6 in a Korean female with ironrefractory iron deficiency anemia. Pediatr. Blood Cancer 2012; 58: 640–42. 10 Beutler E, Van Geet C, te Loo DM et al. Polymorphisms and mutations of human TMPRSS6 in iron deficiency anemia. Blood Cells Mol. Dis. 2010; 44: 16–21. 11 Benyamin B, Ferreira MA, Willemsen G et al. Common variants in TMPRSS6 are associated with iron status and erythrocyte volume. Nat. Genet. 2009; 41: 1173–5. 12 Melis MA, Cau M, Congiu R et al. A mutation in the TMPRSS6 gene, encoding a trans-membrane serine protease that suppresses hepcidin production, in familial iron deficiency anemia refractory to oral iron. Haematologica 2008; 93: 1473–9. 13 Tchou I, Diepold M, Pilotto PA, Swinkels D, Neerman-Arbez M, Beris P. Haematologic data, iron parameters and molecular findings in two new cases of iron-refractory iron deficiency anaemia. Eur. J. Haematol. 2009; 83: 595–602. 14 Edison ES, Athiyarath R, Rajasekar T, Westerman M, Srivastava A, Chandy M. A novel splice site mutation c.2278 (-1) G>C in the
© 2014 Japan Pediatric Society
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TMPRSS6 gene causes deletion of the substrate binding site of the serine protease resulting in refractory iron deficiency anaemia. Br. J. Haematol. 2009; 147: 766–9. Guillem F, Kannengiesser C, Oudin C et al. Inactive matriptase-2 mutants found in IRIDA patients still repress hepcidin in a transfection assay despite having lost their serine protease activity. Hum. Mutat. 2012; 33: 1388–96. Jaspers A, Caers J, Le Gac G et al. A novel mutation in the CUB sequence of matriptase-2 (TMPRSS6) is implicated in ironresistant iron deficiency anaemia (IRIDA). Br. J. Haematol. 2013; 160: 564–5. Ramsay AJ, Quesada V, Sanchez M et al. Matriptase-2 mutations in iron-refractory iron deficiency anemia patients provide new insights into protease activation mechanisms. Hum. Mol. Genet. 2009; 18: 3673–83. Cau M, Galanello R, Giagu N, Melis MA. Responsiveness to oral iron and ascorbic acid in a patient with IRIDA. Blood Cells Mol. Dis. 2012; 48: 121–3. Kemna E, Pickkers P, Nemeth E, Hoeven H, Swinkels D. Timecourse analysis of hepcidin, serum iron, and plasma cytokine levels in humans injected with LPS. Blood 2005; 106: 1864–6. Nemeth E, Rivera S, Gabayan V et al. IL-6 mediates hypoferremia of inflammation by inducing the synthesis of the iron regulatory hormone hepcidin. J. Clin. Invest. 2004; 113: 1271–6. Wu TW, Tabangin M, Kusano R, Ma Y, Ridsdale R, Akinbi H. The utility of serum hepcidin as a biomarker for late-onset neonatal sepsis. J. Pediatr. 2013; 162: 67–71. Cheng HL, Bryant CE, Rooney KB et al. Iron, hepcidin and inflammatory status of young healthy overweight and obese women in Australia. PLoS One 2013; 8: e68675.
Pediatrics International (2014) 56, e41–e44
doi: 10.1111/ped.12395
Patient Report
Novel mutation in the TMPRSS6 gene with iron-refractory iron deficiency anemia Koya Kodama, Atsuko Noguchi, Hiroyuki Adachi, Miwa Hebiguchi, Michihiro Yano and Tsutomu Takahashi Department of Pediatrics, Akita University Graduate School of Medicine, Akita, Japan Abstract
Iron-refractory iron deficiency anemia (IRIDA) is a rare autosomal recessive disease characterized by congenital hypochromic microcytic anemia, low transferrin saturation, low serum iron, normal–high serum ferritin, and increased hepcidin. This disease is caused by loss-of-function mutations in TMPRSS6 that lead to high hepcidin and result in severe anemia. We report our experience with an 11-year-old Japanese girl with hypochromic microcytic anemia, low serum iron, and high serum ferritin, with anemia that was refractory to the oral iron that was prescribed frequently from early childhood. Presence of high hepcidin suggested a diagnosis of IRIDA, which was eventually confirmed by identification of a novel homozygous mutation, p.Pro354Leu, in the TMPRSS6 gene. This case suggests that serum hepcidin should be routinely measured for differential diagnosis when patients with IDA are unresponsive to oral iron or have unusual clinical features.
Key words hepcidin, iron refractory iron deficiency anemia, TMPRSS6.
Iron-refractory iron deficiency anemia (IRIDA) is a rare autosomal recessive disease characterized by congenital hypochromic microcytic anemia, low transferrin saturation, low serum iron, normal–high serum ferritin, and increased hepcidin.1 This disease is caused by mutations in the TMPRSS6 gene, which encodes matriptase-2 (MT2), a member of the type II transmembrane serine protease family that is mainly expressed in the liver.1 TMPRSS6 plays a role in iron metabolism through regulation of the expression of hepcidin, the key protein in iron homeostasis.2 Hepcidin binds to ferroportin, the channel for cellular iron efflux, and induces its internalization and degradation. In patients with IRIDA, high hepcidin, which is caused by defective negative control by TMPRSS6, prevent duodenal absorption and recycling of heme iron by macrophages, resulting in severe anemia. To date, more than 30 TMPRSS6 gene mutations have been identified in patients with IRIDA.3 Correlation between phenotype and genotype has not yet been established in this disease. In this report, we present a case of IRIDA in a Japanese patient caused by a novel homozygous mutation of the TMPRSS6 gene.
Case report An 11-year-old Japanese girl visited hospital because of fatigue and faintness after heavy exercise. On physical examination there were no obvious signs indicating any specific disease, but
Correspondence: Atsuko Noguchi, MD PhD, Department of Pediatrics, Akita Graduate School of Medicine, Akita-shi, Akita 010-8543, Japan. Email: [email protected] Received 5 September 2013; revised 28 February 2014; accepted 24 March 2014.
© 2014 Japan Pediatric Society
laboratory findings showed severe IDA. Laboratory data (Table 1) indicated hypochromic hypovolemic anemia with low serum iron and ferritin, and low saturated transferrin. Clinically, the patient had no fever, appetite had been good and the patient had a balanced diet. There was no occult blood in the stool, and serum Helicobacter pylori antibody was negative. Blood test and urinalysis data indicated no inflammation. Imaging was also normal, therefore various etiologies of anemia, such as intestinal bleeding and chronic inflammation (autoimmune disease, malignant tumor, chronic kidney disease) including H. pylori, were ruled out.
Table 1 Laboratory data Parameter WBC (×103/μL) RBC (×104/μL) Hb (g/dL) Hct (%) MCV (fL) MCH (pg) MCHC (%) Platelets (×103/μL) Reticulocyte (‰) Iron (μg/dL) TIBC (μg/dL) UIBC (μg/dL) Ferritin (ng/mL) Transferrin (mg/dL)
Patient 4.3 506 8.6 29.5 58.3 17 29.2 389 8.8 9 371 362 21.2 243
Reference range 4.0–9.0 380–480 12.0–15.2 34.0–42.0 78.0–110.0 28.0–35.0 31.0–36.0 117–329 7.0–25.0 55–178 245–430 120–340 12.0–60.0 190–320
Hb, hemoglobin; Hct, hematocrit; MCHC, mean corpuscular hemoglobin concentration; MCV, mean corpuscular volume; RBC, red blood cell; TIBC, total iron binding capacity; UIBC, unsaturated iron binding capacity; WBC, white blood cell.
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Before the patient visited hospital, ferrous sulfate was given orally, but IDA was refractory to treatment. Therefore, we diagnosed the patient with IRIDA on the basis of the clinical course and findings. To confirm the diagnosis, we measured serum hepcidin and performed a mutational analysis of TMPRSS6. This study was approved by the ethics committee of Akita University Graduate School of Medicine, and written informed consent was obtained from the patient and her guardian. Serum hepcidin, which was measured using enzyme-linked immunoassay (ELISA) after parenteral iron treatment, was found to be 31.5 ng/mL, (normal range, 7.8 ± 7.0 ng/mL), despite low hemoglobin (Hb; 8.6 g/dL) and low serum iron (5 ng/mL). Mutational analysis of TMPRSS6 identified a novel mutation, c.1175C>T, leading to a replacement of a proline by a leucine at position 354, designated as p.Pro354Leu (Fig. 1). The patient was homozygous whereas her mother was heterozygous for the mutation. The father’s DNA was not available. Given that the patient was diagnosed with IRIDA, we prescribed monthly i.v. iron sucrose (40 mg). After the fourth consecutive treatment, serum ferritin rose from 21.2 to 37.8 ng/mL and Hb increased to 9.3 g/dL.
Discussion We here report a case of IRIDA in a Japanese patient that was caused by a novel homozygous mutation of TMPRSS6 p.Pro354Leu (Fig. 2b). MT2, the protein encoded by TMPRSS6, is composed of a small cytoplasmic domain, a transmembrane domain, a stem region consisting of a sea urchin sperm protein enterokinase agrin (SEA) domain, two C1s/C1r, urchin embryonic growth factor and bone morphogenetic protein-1 (CUB) domains, three low-density lipoprotein receptor class A (LDIRA) domains, and a carboxy-terminal serine protease (SP) domain, listed in order from the N- to the C-terminus.15 MT2 is synthesized as a zymogen that is autoactivated through cleavage by its own trypsin-like serine protease activity. Autoactivation of the zymogen is characterized by cleavage after Arg 576 within a highly conserved Arg-Ile-Val-Gly-Gly (RIVGG) motif located at the junction between the SP domain and the stem. The active
protease is released from the cell membrane into the extracellular medium after a series of steps including multimerization, transactivation, and proteolytic cleavage within the stem. p.Pro354Leu is located at the middle of the second CUB domain of the TMPRSS6 protein. We randomly selected 50 healthy controls with informed consent from Akita Prefectures to determine the minor allele frequency for the identified candidate variants. The haplotype carrying this variant was not observed in 50 controls, nor in any of the publically available databases we examined; we are therefore tempted to speculate that the combination of this variant led to IRIDA in the present patient. To predict the functional effects of the mutation, we performed in silico analysis using PolyPhen-2 (http:// genetics.bwh.harvard.edu/pph2/). This online tool can be used to predict the possible impact of an amino acid substitution on the structure and function of a human protein. The mutation was classified as being “probably damaging”. In addition to PolyPhen-2 analysis, we investigated protein sequence conservation among vertebrates. Pro354 is a highly conserved residue in the CUB domain of TMPRSS6 across different species (Fig. 2a). This further indicated that p.Pro354Leu was a novel mutation. To date, five other mutations responsible for IRIDA have been identified in the second CUB domain of TMPRSS6: p.Y355X,1 p.H369N,16 p.Y393X,8 p.Y418C,15 and p.G442R.1 Mutagenesis and expression studies of p.Y418C showed that although it was characterized by a reduction in autoactivating cleavage, it retained some of its transcriptional repression activity. The precise functional role of the CUB2 domain is yet to be elucidated, but mutations in this domain might cause functional defects in the TMPRSS6 zymogen. The two reports describe successful oral iron therapy in families with IRIDA caused by TMPRSS6 gene mutations. One report described a patient homozygous for the IVS6+1G>C mutation of TMPRSS6, who had responsiveness to oral iron supplemented with ascorbic acid.18 The other report described two siblings with IRIDA who were responsive to continued oral iron therapy without any supplementation.3 These studies indicate the clinical diversity of IRIDA and suggest the possibility of treatment with
Fig. 1 TMPRSS6 genotype in a Japanese patient with iron-refractory iron deficiency anemia. (a) Pedigree of the family. Eu, examination uninformative; P, proband. (b,c) Sequences of exon 9 of the TMPRSS6 gene in (b) the patient and (c) the mother. Arrows: (c) heterozygous nucleotide substitution in the mother; (b) homozygous nucleotide substitution in the patient. The substitution leads to the replacement of a proline by a leucine at position 354 of TMPRSS6, designated as p.Pro354Leu. © 2014 Japan Pediatric Society
Novel TMPRSS6 mutation in a Japanese girl
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Human Chimpanzee Mouse Cow Chicken Zebrafish
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VFQACEVNLTLDNRLDSQGVLSTPYFPSYYSPQTHCSWHLTVPSLDYGLALWFDAYAL VFQACEVNLXLGRWVHQPG--HTPWATWPAPPS-------QVPSLDYGLALWFDAYAL AFQDCQVNLTLEGRLDTQGFLRTPYYPSYYSPSTHCSWHLTVPSLDYGLALWFDAYAL TIQACEVNLTLEGRLEPQGVLSTPYFPSYYSPSTHCSWHLTVPSLDYGLALWFDAYAL PLKACGVNITLREGLELQGKISTPHYPSYYSPNTQCTWHMSVPSLDYGVTLWFDAYAL PDQVCSLSVVLEQTLAVQGVLRTPFYPSYYPPDTNCSWTFTVPSVDYGLTLAFEGYEL
A736V11 P765A15 R774C1
L674F10 P686fs17
K636fs1
G603R9 A605fs1
R599X8
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Fig. 2 (a) Matriptase-2 CUB domain sequences from different species were aligned using Evola version 7.5 (http://www.h-invitational.jp/ evola_main/annotation.cgi?hit=HIT000083936).4 Box, residues corresponding to human proline. Sequences were obtained from the following GenBank entries: human, AY055384; chimpanzee, XR_024662; mouse, AY240929; cow, XM_001255604; chicken, XM_416281; zebrafish, XM_001920132. (b) Matriptase-2 gene/protein structures and locations of IRIDA mutations. Upper panel, encoded protein. Arrows, currently identified iron-refractory iron deficiency anemia (IRIDA) patient mutations on the matriptase-2 protein, corresponding to their genomic locations.5–14 C, C-terminal; CUB, C1s/C1r, urchin embryonic growth factor, and bone morphogenetic protein-1 domain; L, low-densitylipoprotein receptor, class A domain; N, N-terminal domain; SEA, sea urchin sperm protein enterokinase agrin domain; TM, transmembranespanning region. Lower panel, genomic structure of matriptase-2. Black box, coding region; white box, non-coding region.
oral iron therapy. Anemia has a potent influence on quality of life. Given that IRIDA is a rare disease, patients may often fail to be accurately diagnosed. Recently, hepcidin has been recognized as an acute-phase reactant that plays a critical role in inflammation and iron homeostasis.19,20 Serum hepcidin may be a biomarker for several disorders, including infection, inflammatory disease, and even obesity. Therefore, its measurement has become common.21,22 Serum hepcidin should be routinely measured for differential diagnosis when patients with IDA are unresponsive to oral iron therapy or have unusual clinical features.
Acknowledgments The authors thank Harumi Sugawara and Maiko Ito at Akita University School of Medicine for their technical assistance.
References 1 Finberg KE, Heeney MM, Campagna DR et al. Mutations in TMPRSS6 cause iron-refractory iron deficiency anemia (IRIDA). Nat. Genet. 2008; 40: 569–71. 2 Du X, She E, Gelbart T et al. The serine protease TMPRSS6 is required to sense iron deficiency. Science 2008; 320: 1088– 92. 3 Khuong-Quang DA, Schwartzentruber J, Westerman M et al. Iron refractory iron deficiency anemia: Presentation with hyperferritinemia and response to oral iron therapy. Pediatrics 2013; 131: e620–25. 4 Matsuya A, Sakate R, Kawahara Y et al. Evola: Ortholog database of all human genes in H-InvDB with manual curation of phylogenetic trees. Nucleic Acids Res. 2008; 36: D787– 92. 5 Altamura S, D’Alessio F, Selle B, Muckenthaler MU. A novel TMPRSS6 mutation that prevents protease auto-activation causes IRIDA. Biochem. J. 2010; 431: 363–71.
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