Hemochromatosis Locus Research Articles

Juvenile hemochromatosis locus maps to chromosome 1q in a French Canadian population.

Juvenile hemochromatosis (JH) is a rare autosomal recessive disorder that causes iron overload. In the French Canadian region of Saguenay Lac-Saint-Jean the worldwide largest cohort of JH cases has been identified. Here, we report the mapping of this large cohort of cases to the HFE2 locus on chromosome 1q. A maximum multipoint location score of 7.02 was observed with marker D1S2344. A common ancestral haplotype, showing the presence of a founder effect, was identified. The analysis of recombinants allowed us to confirm the JH candidate region.

Juvenile hemochromatosis

Juvenile hemochromatosis or type 2 hemochromatosis is a rare inherited recessive disease, which leads to severe iron overload earlier in life than HFE-related hemochromatosis. Increased transferrin saturation and serum ferritin as well as parenchymal iron deposition and liver fibrosis may be observed in childhood. Clinical symptoms of hypogonadism and cardiac disease develop before the age of 30. The disease is usually progressive and if untreated may become fatal because of heart failure. The type 2 hemochromatosis locus maps to chromosome 1q21, but the gene has not yet been isolated. The severity and the early expression of juvenile hemochromatosis suggest that the gene product has a crucial role in the regulation of iron homeostasis. Semin Hematol 39:242-248. Copyright 2002, Elsevier Science (USA). All rights reserved.

Allelic association of microsatellites of 6p in Italian hemochromatosis patients.

Hemochromatosis (HC) is an inherited disorder of iron metabolism and is frequently seen in Caucasians. The biochemical defect and the responsible gene are unknown, but the HC locus is closely linked to HLA-A on human chromosome 6 in the region 6p21.3. Although extensive studies have been performed in several populations, the precise location of the gene is still undefined. Linkage disequilibrium with HC has been detected for loci that are 3 cM apart: HLA class I and D6S105, which is located on the telomeric side of HLA-A. We have analyzed the inheritance of several multi-allele polymorphisms that map to 6p (D6S265, Y52, HLA-F, D6S306, D6S105, D6S464, D6S299) in 34 Italian HC families and in 17 unrelated patients. Significant association with HC was shown for alleles of multiple markers in the HLA-A region, for the distant marker D6S105, but not for the D6S299 marker at 4 cM from HLA-A on the telomeric side. HC status was unambiguously assigned to 70 affected and 63 unaffected chromosomes from family studies. Thirty five different haplotypes were found in 70 HC chromosomes when considering four markers most tightly associated with the disease. A predominant haplotype comprising alleles 1-3-1-8 (marker order D6S265, HLA-A, Y52, D6S105) accounted for 30% of the HC chromosomes and was absent in normals. A minority of other HC haplotypes could be related to the major haplotype by assuming single crossover events. Results of haplotype studies suggest a founder effect in the Italian population, as previously shown in Australian patients, and a possible common mutation shared with affected individuals of Celtic origin.

Localization of the Hemochromatosis Disease Gene: Linkage Disequilibrium Analysis Using an American Patient Collection

ABSTRACT The genetic basis of idiopathic hemochromatosis, a common disorder of iron metabolism, has remained an enigma for over two decades. In an attempt to refine the chromosomal localization of this gene, we have conducted a linkage disequilibrium mapping study utilizing a large group of unrelated American patients. The 12 microsatellites used as genetic markers in this analysis include a series of recently described polymorphic dinucleotide (D6S1558, D6S1545 and D6S1554) and tetranucleotide (D6S1016 and D6S1281) repeats which map between D6S105 and D6S299. Haplotype reconstructions indicate that a core genotype, composed of D6S464 allele 3/D6S1260 allele 4/D6S1558 allele 5, exists on a majority of disease chromosomes. Stringent statistical measures of marker-disease disequilibrium suggest that only associations with D6S1260 are significant and furthermore, aid in the assignment of refined centromeric and telomeric limits for the likely location of the hemochromatosis gene. In summary, the genetic data presented in this report predict that the hemochromatosis locus resides between D6S464 and D6S1558, most likely very close to marker D6S1260. Because a single yeast artificial chromosome clone contains all three of the above loci, a thorough search for coding sequences in this region is likely to identify the gene mutated in this common disorder.

Allelic association of microsatellites of 6p in Italian hemochromatosis patients

Hemochromatosis (HC) is an inherited disorder of iron metabolism and is frequently seen in Caucasians. The biochemical defect and the responsible gene are unknown, but the HC locus is closely linked to HLA-A on human chromosome 6 in the region 6p21.3. Although extensive studies have been performed in several populations, the precise location of the gene is still undefined. Linkage disequilibrium with HC has been detected for loci that are 3 cM apart: HLA class I and D6S105, which is located on the telomeric side of HLA-A. We have analyzed the inheritance of several multi-allele polymorphisms that map to 6p (D6S265, Y52, HLA-F, D6S306, D6S105, D6S464, D6S299) in 34 Italian HC families and in 17 unrelated patients. Significant association with HC was shown for alleles of multiple markers in the HLA-A region, for the distant marker D6S 105, but not for the D6S299 marker at 4 cM from HLA-A on the telomeric side. HC status was unambiguously assigned to 70 affected and 63 unaffected chromosomes from family studies. Thirty five different haplotypes were found in 70 HC chromosomes when considering four markers most tighly associated with the disease. A predominant haplotype comprising alleles 1-3-1-8 (marker order D6S265, HLA-A, Y52, D6S 105) accounted for 30% of the HC chromosomes and was absent in normals. A minority of other HC haplotypes could be related to the major haplotype by assuming single crossover events. Results of haplotype studies suggest a founder effect in the Italian population, as previously shown in Australian patients, and a possible common mutation shared with affected individuals of Celtic origin.

Exclusion of ferritins and iron-responsive element (IRE)-binding proteins as candidates for the hemochromatosis gene.

We have looked for genes for ferritin and its translational control protein that could account for anomalies in the expression of ferritin (FT) and the transferrin receptor in the duodenum of individuals with hemochromatosis (HC). We show that there are probably only two FTH-like sequences near the HC locus on the short arm of chromosome 6 and no FTL-like sequences. We report the cloning of the previously uncharacterized FTH sequence from 6p (FTHL15) and show that it is probably a processed pseudogene. This gene has been mapped with a panel of radiation hybrid cells to near 6p12. Additionally, we show that there are no sequences on chromosome 6p for a protein that coordinately regulates expression of ferritin and the transferrin receptor.

Expression of hemochromatosis in homozygous subjects: Implications for early diagnosis and prevention

This study looks at expression of genetic hemochromatosis in the homozygous and heterozygous states. Two hundred nine subjects in 40 families with confirmed hemochromatosis and clear evidence of HLA linkage in symptomatic individuals were studied prospectively for up to 24 yr. The study group consisted of 40 probands, 51 subjects sharing two HLA haplotypes with affected relatives (putative homozygotes), 98 putative heterozygotes, and 20 putative normal homozygotes. Forty-eight of 51 subjects predicted to be homozygous showed increased hepatic iron stores as assessed by liver biopsy and quantitative phlebotomy. If not evident initially, this developed in 1–8 yr. In the 3 subjects predicted by HLA typing to be homozygous but in whom there was no progressive iron accumulation, results of studies using another chromosome 6 genetic marker (Factor 13 A subunit) were consistent with chromosomal recombination, presumably separating one hemochromatosis allele from the HLA markers. No heterozygous subject developed overt hemochromatosis during the period of follow-up, although 1 showed evidence of iron overload at initial assessment. Genetic recombination is again thought to have separated the hemochromatosis allele from the HLA markers here. The present findings favor a location of the hemochromatosis locus telomeric to HLA-A. It is concluded that, in this population, hemochromatosis is apparently always HLA linked, and homozygous subjects will develop iron overload in the absence of chromosomal recombination or blood loss.

Serum Ferritin as a Marker of Affection for Genetic Hemochromatosis

A bivariate segregation analysis of genetic hemochromatosis with serum ferritin concentration was undertaken to examine the pleiotropic effect of the hemochromatosis locus on each of the two phenotypes, in an ascertained sample of families from Brittany, France. The gene was recessive with respect to both phenotypes, and the estimated gene frequency in the general population was 0.054. Although the ferritin concentration was corrected for the linear relationship with age among controls, there was a residual correlation with age among male family members, consistent with the progressive increase in body iron stores among hemochromatosis homozygotes. This genotype-specific relationship with age illustrates the importance of incorporating interaction effects into analytic models, and suggests that even as a better indicator of progress of disease, rather than liability to disease, serum ferritin concentration serves well to distinguish hemochromatosis homozygotes from alternate genotypes in a family study.

Hereditary Hemochromatosis: Analysis of Laboratory Expression of the Disease by Genotype in 18 Pedigrees

Tight linkage between the hemochromatosis locus and the HLA region permits determination of genotype in members of hemochromatosis pedigrees. To determine if simple laboratory measures of iron metabolism could predict the affected genotype without the need for HLA typing, we studied seven measures of iron metabolism: serum iron concentration, total iron-binding capacity, per cent saturation of transferrin, serum ferritin concentration, deferoxamine-induced urinary iron excretion and hepatic iron concentration evaluated by both chemical and histological methods. Discriminant analysis showed a per cent saturation of transferrin above 62% to be the best simply-measured indicator of the affected genotype: homozygosity is accurately predicted in 92% of the cases. The logarithmic transform of serum ferritin concentration was only 71% accurate. Pedigree analysis estimated the frequency of the hemochromatosis gene at 0.069 +/- 0.020 with a recombination probability of 0.015 +/- 0.015 with the HLA region. This corresponds to a heterozygote frequency of 0.13 and a disease frequency of 0.005.

Genetic mapping of the hemochromatosis locus on chromosome six

The purpose of this paper is to report a pedigree with hereditary hemochromatosis in which a recombination between the HLA-A and B loci occurred. Both the maternal and paternal HLA-A3, B7 haplotypes were carrying an allele for hemochromatosis. The A3, B12 haplotype of the proband was a recombinant of the maternal A3, B7 and A28, B12 haplotypes. The hemochromatosis locus segregated with the HLA-A locus and not with the HLA-B locus. Thus, the hemochromatosis locus maps in close proximity to the HLA-A locus.