No abstract

The gene whose alteration causes hereditary hemochromatosis (HFE according to the international nomenclature) was, more than 20 years ago, shown to map to 6p21.3. It has since escaped all efforts to identify it by positional cloning strategies. Quite recently, a gene named HLA-H was reported as being responsible for the disease. Two missense mutations, Cys282Tyr (C282Y) and His63Asp (H63D), were observed, but no proof was produced that the gene described is the hemochromatosis gene. To validate this gene as the actual site of the alteration causing hemochromatosis, we decided to look for the two mutations in 132 unrelated patients from Brittany. Our results indicate that more than 92% of these patients are homozygous for the C282Y mutation, and that all 264 chromosomes but 5 carry either mutation. These findings confirm the direct implication of HLA-H in hemochromatosis.

present in 70% of homozygotes, and an extended ancestral A candidate gene (HFE) has been described for hereditary haplotype including HLA-A3 and other DNA markers on hemochromatosis on chromosome 6. The study of well-dechromosome 6 has been reported. [5][6][7] A candidate gene has fined atypical hemochromatosis families using genetic markbeen described (HFE), 4.5 Mb telomeric to HLA-A. 8 The use ers may increase our understanding of the sensitivity and the of haplotype analysis and the search for recombinations in specificity of genotyping in hemochromatosis. One hundred families are considered to be powerful tools for localizing a and thirteen Canadian families with genetic hemochromatosis gene responsible for a disease. However, in hemochromatowere surveyed to find atypical families as possible examples sis, it had been difficult to prove informative genetic recombiof people with genetic recombinations. All families underwent nations for several reasons: 1) the late presentation of the clinical investigations including iron studies and HLA typing.probands in the fifth or sixth decade often means that parenEach individual was typed at three polymorphic microsatellite tal DNA is not available; 2) ascertainment of the phenotypic loci (D6S105, D6S1260, and D6S299) on chromosome 6. Sixstatus may be difficult and may vary between studies; and teen subjects were studied for the two missense mutations 3) lack of heterogeneity with available DNA markers has described for the candidate gene for hemochromatosis reduced the number of informative family studies. In this (C282Y, H63D). There were eight HLA-identical siblings study, 113 Canadian families with genetic hemochromatosis found in four different families (five men, three women; age were reviewed, and DNA studies are presented in 5 atypical range 30-72) with normal transferrin saturation and ferritin families with potential recombinations. levels. There were two patients identified who were homozy- PATIENTS AND METHODS gous for the C282Y mutation without biochemical evidenceA database of 113 Canadian families that had been investigated of iron overload, and two patients with no evidence of the by family studies was reviewed to search for families with potential mutation with significant iron overload. Our conclusions are genetic recombinations. All families were white with European anas follows: 1) finding HLA-identical siblings without iron overcestry. This study included 4 families in which one or more HLAload does not confirm a genetic recombination, 2) difficulties identical sibling was found without phenotypic expression of the in phenotypic definition of disease and the description of new disease, and 1 family in which two putative homozygotes produced iron overload syndromes that may differ from classical genetic an unaffected son. The diagnosis of hemochromatosis was based HC cause complicated genetic studies, and 3) finding iron-on clinical history, physical examination, and elevated serum ferriloaded patients without a C282Y mutation and patients that tin...

The hemochromatosis gene (HFE) maps to 6p21.3, in close linkage with the HLA Class I genes. Linkage disequilibrium (LD) studies were designed to narrow down the most likely candidate region for HFE, as an alternative to traditional linkage analysis. However, both the HLA-A and D6S105 subregions, which are situated 2-3 cM and approximately 3 Mb apart, have been suggested to contain HFE. The present report extends our previous study based upon the analysis of a large number of HFE and normal chromosomes from 66 families of Breton ancestry. In addition to the previously used RFLP markers spanning the 400-kb surrounding HLA-A, we examined three microsatellites: D6S510, HLA-F, and D6S105. Our combined data not only confirm a peak of LD at D6S105, but also reveal a complex pattern of LD over the i82 to D6S105 interval. Within our ethnically well-defined population of Brittany, the association of HFE with D6S105 is as great as that with HLA-A, while the internal markers display a lower LD. Fine haplotype analysis enabled us to identify two categories of haplotypes segregating with HFE. In contrast to the vast majority of normal haplotypes, 50% of HFE haplotypes are completely conserved over the HLA-A to D6S105 interval. These haplotypes could have been conserved through recombination suppression, selective forces and/or other evolutionary factors. This particular haplotypic configuration might account for the apparent inconsistencies between genetic linkage and LD data, and additionally greatly complicates positional cloning of HFE through disequilibrium mapping.