Iron overload in HFE C282Y heterozygotes at first genetic testing: a strategy for identifying rare HFE variants

Abstract

Background: Heterozygotes for the p.Cys282Tyr (C282Y) mutation of the HFE gene do not usually express a hemochromatosis phenotype. Apart from the compound heterozygous state for C282Y and the widespread p.His63Asp (H63D) variant allele, other rare HFE mutations can be found in trans on chromosome 6.

Design and methods: We performed molecular investigation of the genes implicated in hereditary hemochromatosis in six patients who presented with iron overload but were simple heterozygotes for the HFE C282Y mutation at first genetic testing. Functional impairment of new variants was deduced from computational methods including molecular modeling studies.

Results: We identified four rare HFE mutant alleles, three of which have not been previously described. One mutation is a 13-nucleotide deletion in exon 6 (c.1022_1034del13, p.His341_Ala345 > LeufsX119), which is predicted to lead to an elongated and unstable protein. The second one is a substitution of the last nucleotide of exon 2 (c.340G > A, p.Glu114Lys) which modifies the relative solvent accessibility in a loop interface. The third mutation, p.Arg67Cys, also lies in exon 2 and introduces a destabilization of the secondary structure within a loop of the α1 domain. We also found the previously reported c.548T > C (p.Leu183Pro) missense mutation in exon 3. No other known iron genes were mutated. We present an algorithm at the clinical and genetic levels for identifying patients deserving further investigation. Conclusions Our results suggest that additional mutations in HFE may have a clinical impact in C282Y carriers. In conjunction with results from previously described cases we conclude that an elevated transferrin saturation level and elevated hepatic iron index should indicate the utility of searching for further HFE mutations in C282Y heterozygotes prior to other iron gene studies.

Figure 1.

Known and new private mutations described on the HFE gene in trans to C282Y. Schematic representation of the HFE gene showing the location of the mutations described in association with p.C282Y (in trans). Nonsense, frameshift and splice mutations are in the upper panel, whereas missense mutations are in the lower panel. Newly identified mutations (this study) are underlined. Most identified missense mutations (indicated by an asterisk) affect key residues presumably involved in HFE-TfR1 binding thus leading to severely disturbed protein function. The p.Q283P mutation is predicted to destabilize the HFE protein. α1, α2 and α3 represent the three extracellular domains of the HFE protein.