DMT1 genetic variability is not responsible for phenotype variability in hereditary hemochromatosis

Homozygosity for a cysteine to tyrosine translocation at position 282 within the HFE gene (C282Y) is responsible for over 90% of hereditary hemochromatosis (HH) in Celtic populations. Determining those C282Y homozygotes at greatest risk for iron overload is a major clinical concern as only a small percentage will develop clinically significant iron overload. Divalent metal transport protein (DMT1) on the apical surface of duodenal enterocytes is recognised as the major iron import protein. We investigated whether genetic variability within the DMT1 gene may partly explain the phenotypic variability seen amongst a group of C282Y homozygotes with iron overload.

One hundred and one unrelated C282Y homozygotes and 103 C282Y negative controls were analysed for the presence of four specific mutations/polymorphisms within the DMT1 gene (1245T/C, 1303C/A, IVS4 + 44C/A, IVS15Ex16-16C/G) using standard PCR techniques. Hepatic iron deposition was determined in 32 HH patients following Perls Prussian blue staining (0-4+). Estimations of the haplotype frequencies were performed utilising the program Arlequin version 2.

There were no significant differences in the allele frequencies of the IVS4 + 44C/A, 1303C/A, 1254T/C and IVS15Ex16-16C/G polymorphisms in the patient cohort compared to those observed in the control cohort. The commonest haplotypes identified were CCTC: IVS4C + 44C, 1303C, 1254T, IVS15ex16-16C; ACCC: IVS4C + 44A, 1303C, 1254C, IVS15ex16-16C and ACTG: IVS4C + 44A, 1303C, 1254T, IVS15ex16-16G. Similarly, there were no significant differences in the frequencies of these three haplotypes in the patient cohorts (regardless of the degree of hepatic iron deposition) compared to the control cohort.

Polymorphisms within DMT1 gene do not influence penetrance of the HH phenotype.