Hélène Coppin

Mutations in the MHC class I-like candidate gene for hemochromatosis in French patients.

Abstract A candidate gene for hemochromatosis has recently been localized on the short arm of chromosome 6, about 4 megabases telomeric to the major histocompatibility complex. It encodes a protein that exhibits significant similarity to the HLA class I molecules and can be provisionally designated HLA-hc. Genotype analysis of 94 hemochromatosis patients living in France and a similar number of controls confirms that the disease is strongly associated with homozygosity at nucleotide 845 (72% of the patients and none of the controls carry two copies of the 845A variant). The data are consistent with hemochromatosis being a heterogeneous disease: about 79% of the cases in this sample would be caused by a defect in HLA-hc and 21% by an unrelated mechanism. A second variant (187 G) enriched on patient chromosomes that do not carry the 845A mutation might influence the affinity of a ligand for HLA-hc; the exact nature of this ligand remains to be discovered. The 845A variant is the best genetic marker for the disease identified to date, and the detection of 845A homozygosity should now permit diagnosis of a readily curable disease and the prevention of sometimes deadly complications in at least 72% of the patients.

BMP/Smad signaling is not enhanced in Hfe-deficient mice despite increased Bmp6 expression

Impaired regulation of hepcidin expression in response to iron loading appears to be the pathogenic mechanism for hereditary hemochromatosis. Iron normally induces expression of the BMP6 ligand, which, in turn, activates the BMP/Smad signaling cascade directing hepcidin expression. The molecular function of the HFE protein, involved in the most common form of hereditary hemochromatosis, is still unknown. We have used Hfe-deficient mice of different genetic backgrounds to test whether HFE has a role in the signaling cascade induced by BMP6. At 7 weeks of age, these mice have accumulated iron in their liver and have increased Bmp6 mRNA and protein. However, in contrast to mice with secondary iron overload, levels of phosphorylated Smads 1/5/8 and of Id1 mRNA, both indicators of BMP signaling, are not significantly higher in the liver of these mice than in wild-type livers. As a consequence, hepcidin mRNA levels in Hfe-deficient mice are similar or marginally reduced, compared with 7-week-old wild-type mice. The inappropriately low levels of Id1 and hepcidin mRNA observed at weaning further suggest that Hfe deficiency triggers iron overload by impairing hepatic Bmp/Smad signaling. HFE therefore appears to facilitate signal transduction induced by the BMP6 ligand.

Absence of the hemochromatosis gene Cys282Tyr mutation in three ethnic groups from Algeria (Mzab), Ethiopia, and Senegal

Abstract A Celtic origin for hemochromatosis, a common genetic iron metabolism disorder, has been postulated for a long time. To check whether the two mutations recently identified in the HLA-class I candidate gene for this disease were found only in Caucasians, we examined their frequencies in individuals originating from Algeria, Ethiopia, and Senegal. The presumably disease-causing mutation, responsible for the Cys282Tyr substitution, was not found in any member of these ethnic groups, although it was shown to be highly prevalent in populations of European ancestry. This geographic distribution supports the previously suggested Celtic origin for the disease. In contrast, the mutation responsible for the His63Asp substitution is not restricted to European populations. Although absent in the Senegalese, it was found on about 9% of the chromosomes of the Central Ethiopians and Algerians (Mzab) genotyped for this study. This second mutation, which probably represents a common variant unrelated to hemochromatosis, thus appears to have occurred earlier than that responsible for the Cys282Tyr substitution. More detailed population studies are needed to provide information on the age of these two mutations and eventually show how the hemochromatosis-causing mutation chronologically spread throughout Europe.

Longevity and carrying the C282Y mutation for haemochromatosis on the HFE gene: case control study of 492 French centenarians.

Hereditary haemochromatosis is a common autosomal recessive disorder of iron metabolism. Most patients are homozygous for a C282Y mutation in the HFE gene. This mutation is frequent in northern Europe, where one in five to ten people are carriers. People who are heterozygous for the C282Y mutation have slightly but significantly higher values for serum iron and transferrin saturation and are less likely to have anaemia because of iron deficiency.1 2 Iron promotes the generation of free radicals, which leads to mutagenesis, atherosclerosis, inflammation, and bacterial growth. Therefore, genotypes that increase the concentrations of iron for transport and storage may be associated with an increased risk for common diseases, such as cancers and cardiovascular diseases, and for inflammatory and infectious conditions. Other studies, which investigated the associations of C282Y heterozygosity with morbidity, found conflicting …

Myelin oligodendrocyte glycoprotein (MOG) gene polymorphisms and multiple sclerosis: no evidence of disease association with MOG

The region surrounding the myelin oligodendrocyte glycoprotein (MOG) gene, located telomeric to the major histocompatibility complex on chromosome 6, was shown to contain three highly informative microsatellites. To examine the potential role of variants of the MOG gene in susceptibility to multiple sclerosis, these CA-repeat polymorphic markers were characterized on a sample of 169 multiple sclerosis patients and 173 healthy unrelated individuals by a method combining fluorescence labelling of PCR products and use of an automated DNA sequencer. Both patients and controls lived in the southwest of France (in the Pyrenees-Atlantiques) and had similar ethnic background. The distribution of the MOG haplotypes was not significantly different in the two groups (P = 0.38). This is not in favour of the implication of the MOG gene in the genetic component of multiple sclerosis, unless different independent mutations have occurred within this gene.

Iron overload induces Bmp6 expression in the liver but not in the duodenum

Background The bone morphogenetic protein BMP6 regulates hepcidin production by the liver. However, it is not yet known whether BMP6 derives from the liver itself or from other sources such as the small intestine, as has been recently suggested. This study was aimed at investigating the source of BMP6 further. Design and Methods We used three different strains of mice (C57BL/6, DBA/2, and 129/Sv) with iron overload induced either by an iron-enriched diet or by inactivation of the Hfe gene. We examined Bmp6 expression at both the mRNA (by quantitative PCR) and protein (by immunohistochemistry and Western blotting analyses) levels. Results We showed that iron overload induces Bmp6 mRNA expression in the liver but not in the duodenum of these mice. Bmp6 is also detected by immunohistochemistry in liver tissue sections of mice with iron overload induced either by an iron-enriched diet or by inactivation of the Hfe gene, but not in liver tissue sections from iron-loaded Bmp6-deficient mice. Bmp6 in the duodenum was below immunodetection threshold, thus confirming quantitative PCR data. Lack of specificity of available antibodies together with slight heterogeneity between 129 substrains may account for the differences with previously published data. Conclusions Our data strongly support the importance of liver BMP6 for regulation of iron metabolism. Indeed, they demonstrate that intestinal Bmp6 expression is modulated by iron neither at the mRNA nor at the protein level.

Investigation of seven proposed regions of linkage in multiple sclerosis: An American and French collaborative study

Abstract.Multiple sclerosis (MS) is a demyelinating autoimmune disease with a strong yet complex genetic component. To date only the HLA-DR locus, and specifically the HLA-DR15 allele, has been identified and confirmed as influencing the risk of developing MS. Genomic screens on several datasets have been performed and have identified several chromosomal regions with interesting results, but none have yet been confirmed. We tested seven of the most-promising regions (on chromosomes 1p, 2p, 3p, 3q, 5q, 19q, and Xp) identified from several genomic screens in a dataset of 98 multiplex MS families from the United States and 90 multiplex MS families from France. The results did not confirm linkage to 2p, 3q, 5q, or Xp in the overall dataset, or in subsets defined by geographic origin or HLA-DR15 status. Regions on 1p34, 3p14, and 19q13 produced lod scores >0.90 in at least one subset of the data, suggesting that these regions should be examined in more detail.

Use of Denaturing HPLC and a Heteroduplex Generator to Detect the HFE C282Y Mutation Associated with Genetic Hemochromatosis

Hereditary hemochromatosis (HH) is a common autosomal recessive disorder of iron metabolism. Most individuals with HH are homozygous for a 845G→A missense mutation (C282Y) in the HFE gene that encodes a MHC class I-like protein (1)(2)(3)(4)(5). One in 300 adults of Caucasian descent has this genotype (3)(6). The disease is characterized by increased absorption of dietary iron by the gastrointestinal tract and the progressive deposition of iron in the parenchymal cells. It produces a wide range of clinical complications, including hepatic fibrosis, cirrhosis, hepatocellular carcinoma, diabetes mellitus, hypopituitarism, hypogonadism, arthritis, and cardiomyopathy (7). These complications can be entirely prevented with regular iron removal by phlebotomy. The availability of this effective treatment highlights the value of screening appropriate populations for the C282Y mutation to detect HH before irreversible complications occur (8). Another frequent mutation in the HFE gene, H63D, has been described (1), but the relationship between this mutation and iron overload is less clear. Although compound heterozygotes C282Y/H63D (1) and H63D homozygotes (9) may show some degree of iron overload, the penetrance associated with these genotypes is very low, and clinical features of hemochromatosis, especially liver disease, are rare. In opposition to C282Y, screening the population for H63D is therefore not indicated. An important issue is the development of a cost-effective methodology suitable for genetically testing large numbers of samples for the C282Y mutation. Many methods have been used to detect C282Y, including oligonucleotide ligation assays (1), fragment length polymorphism analyses of PCR products after restriction enzyme digestion (5), allele-specific oligonucleotide hybridization assays (2), mutagenically separated PCR assays (10), primer extension assays (11)(12), and allele refractory mutation systems (13)(14). All of these assays are time-consuming. In addition, they rely on complicated multistep procedures involving radioisotopes or …

No evidence for transmission disequilibrium between a new marker at the myelin basic protein locus and multiple sclerosis in French patients.

The myelin basic protein (MBP) gene is a candidate locus for susceptibility to multiple sclerosis. Several groups have tested a complex (TGGA)n repeat in the 5′ region of this gene for association/linkage with multiple sclerosis, with divergent results. This region of tandem repetitive sequence has been subjected to complex rearrangements, and there is a possibility that alleles of the same size have different internal structures, which reduces the interest of this marker for linkage disequilibrium studies and may at least partly explain the conflicting results obtained so far. To overcome this problem, we isolated a new polymorphic (CA)n repeat within the Golli-MBP locus. The limited number of alleles identified makes this other marker suitable for transmission disequilibrium studies. We tested this marker for linkage with multiple sclerosis, using the transmission-disequilibrium test (TDT) on a sample of 196 nuclear families in which the genotypes of both parents could be unambiguously defined. We found no evidence of transmission disequilibrium between multiple sclerosis and any of the three alleles of this marker, even when the patients were subdivided according to their HLA-DRB1*1501 status. The present data thus provide no evidence for a contribution of the MBP gene to multiple sclerosis susceptibility in French patients.