Novel TMPRSS6 mutations associated with iron-refractory iron deficiency anemia (IRIDA)

Abstract

Mutations leading to abrogation of matriptase-2 proteolytic activity in humans are associated with an iron-refractory iron deficiency anemia (IRIDA) due to elevated hepcidin levels. In this paper we describe 12 IRIDA patients belonging to 7 unrelated families and identify 10 (9 novel) TMPRSS6 mutations spread along the gene sequence: 5 missense, 1 non sense and 4 frameshift. The frameshift and non sense mutations are predict to result in truncated protein lacking the catalytic domain. The causal role of missense mutations (Y141C, I212T, R271Q, S304L and C510S) is demonstrated by in silico analysis, their absence in 100 control chromosomes and the high conservation of the involved residues. The C510S mutation in the LDLRA domain in silico model causes an intra-molecular structural imbalance that impairs matriptase-2 activation. We also assessed the in vitro effect on hepcidin promoter and the proteolytic activity of I212T and R271Q variants demonstrating a reduced inhibitory effect for the former mutation, but surprisingly a normal function for R271Q which appears a silent mutation in vitro. Based on mRNA expression studies I212T could also decrease the total amount of protein produced, likely interfering with mRNA stability. Collectively, our results extend the pattern of TMPRSS6 mutations associated with IRIDA and propose a model of causality for some of the novel missense mutation. ©2010Wiley-Liss, Inc.

Iron refractory iron deficiency anemia

“…When IRIDA patients show very low Hb levels and increased number of RBCs, 48,49 a helpful marker for a differential diagnosis is the reticulocyte count, which is high in betathalassemia and low in IRIDA.…”

Deletion of TMPRSS6 attenuates the phenotype in a mouse model of β-thalassemia

“…[12][13][14][15][16][17] The important role of TMPRSS6 in erythropoiesis is highlighted also by genome-wide association studies. Common TMPRSS6 genetic variants, such as rs855791, associate with serum iron and transferrin saturation, hemoglobin (Hb), and erythrocyte (MCV and MCH) traits in different populations.…”

Inactive matriptase-2 mutants found in IRIDA patients still repress hepcidin in a transfection assay despite having lost their serine protease activity

“…The active protease is released from the cell membrane into the extracellular medium by proteolytic cleavage within the stem . So far, 34 MT2 mutations have been identified in human patients with IRIDA [Altamura et al, 2010;Beutler et al, 2009;Choi et al, 2011;De Falco et al, 2010;Edison et al, 2009;Finberg et al, 2008;Guillem et al, 2008;Melis et al, 2008;Ramsay et al, 2009b;Sato et al, 2011;Silvestri et al, 2009;Tchou et al, 2009]. These include missense, nonsense, frameshift, and splice junction mutations.…”

“…These include missense, nonsense, frameshift, and splice junction mutations. Missense mutations have been found in several different protein domains of the extracellular part of the zymogen, and some of them have been further characterized by transfection experiments, usually by assessing the ability of mutated proteins to repress the hepcidin promoter linked to a luciferase reporter gene [Altamura et al, 2010;De Falco et al, 2010;Du et al, 2008;Ramsay et al, 2009b;Silvestri et al, 2008Silvestri et al, , 2009. Here, we describe five mutations observed in IRIDA patients, one homozygous frameshift mutation, found in one family, and four missense mutations located in the CUB1, CUB2, SEA, and SP domains of MT2, found in two families with compound heterozygosity of the affected children.…”