[Hereditary iron overload]. / Surcharges héréditaires en fer.

The field of hereditary iron overload has known, in the recent period, deep changes mainly related to major advances in molecular biology. It encompasses now a series of genetic entities. The mechanistic understanding of iron overload development and iron toxicity has greatly improved. The diagnostic approach has become essentially noninvasive with a major role for biological tests. From the therapeutic viewpoint, the phlebotomy treatment is now enriched by the possibility of resorting to oral chelation and by innovative perspectives directly linked to our improvement in the molecular understanding of these diseases.

The 16189 variant of mitochondrial DNA occurs more frequently in C282Y homozygotes with haemochromatosis than those without iron loading.

BACKGROUND: Patients with hereditary haemochromatosis (HH) are usually homozygous for the C282Y mutation in the HFE gene. They have variable expression of iron overload and present with a variety of complications, including liver disease, diabetes, arthropathy, fatigue, and cardiomyopathy. The mitochondrial 16189 variant is associated with diabetes, dilated cardiomyopathy, and low body fat at birth, and might contribute to genetic predisposition in further multifactorial disorders. The objective of this study was to determine the frequency of the 16189 variant in a range of patients with haemochromatosis, who had mutations in the HFE gene. METHODS: Blood DNA was analysed for the presence of the 16189 variant in British, French, and Australian C282Y homozygotes and controls, with known iron status, and in birth cohorts. RESULTS: The frequency of the mitochondrial 16189 variant was found to be elevated in individuals with haemochromatosis who were homozygous for the C282Y allele, compared with population controls and with C282Y homozygotes who were asymptomatic (42/292 (14.4%); 102/1186 (8.6%) (p = 0.003); and 2/64 (3.1%) (p = 0.023), respectively). CONCLUSIONS: Iron loading in C282Y homozygotes with HH was exacerbated by the presence of the mitochondrial 16189 variant.

Serum paraoxonase activity and paraoxonase gene polymorphism in type 2 diabetic patients with or without vascular complications.

BACKGROUND: Serum paraoxonase (PON) activity and the relevance of PON gene polymorphism in vascular complications of type 2 diabetic patients were investigated in a case-control study. METHODS: The population included 105 control subjects, 96 diabetic patients without vascular complications and 71 diabetics with vascular complications. RESULTS: Serum PON activity was significantly decreased (p<0.001) in diabetic patients without vascular complications: 207 IU (25-817) compared with the controls: 259 IU (24-950). Although serum PON activity was also decreased: 232 IU (34-797) in the population with vascular complications, the difference was not statistically significant (p=0.11). The Q192 allele frequency is significantly higher (p<0.005) in diabetics without vascular complications (77%), and with vascular complications (73%) than in the controls (63%). No significant association was found between either PON(1)55 L/M and PON(2)311 C/S gene polymorphisms and vascular complications. CONCLUSIONS: The difference in allele frequency for the PON(1) Q/R 192 gene polymorphism may be the cause of the low paraoxonase activity observed in type 2 diabetes mellitus. Further studies need to be conducted to elucidate the role of the enzyme in the development of vascular complications in diabetes.

Geography of HFE C282Y and H63D mutations.

Hereditary hemochromatosis (HH) is a common autosomal recessive disorder causing inappropriate dietary iron absorption that affects North Europeans. HH is associated with the C282Y mutation of the HFE gene, and the H63D mutation to a lesser degree. Both mutations are abundant in Europe, with H63D also appearing in North Africa, the Middle East, and Asia. Emigration from Europe over the past 500 years has introduced C282Y and H63D to America, Australia, New Zealand, and South Africa in an essentially predictable fashion. The distinctive characteristics of the population genetics of HH are the confined racial distribution and high frequency in North European peoples. C282Y frequencies in North Europeans are typically between 5% and 10%, with homozygotes accounting for between 1/100 and 1/400 of these populations. The scarcity of the C282Y mutation in other populations accounts for the lack of HH in non-Europeans.

[Genetic hemochromatosis]. / Hémochromatose génétique.

Haemochromatosis is the most common genetic disease in individuals of Northern European origin. This disorder of iron metabolism, for which the molecular basis remains poorly understood, is characterized by an excessive absorption of dietary iron through the duodenal mucosa. Progressive iron loading of parenchymal organs results in the mid-life onset of clinical complications, and patients may succumb to cardiac failure and/or hepato-carcinoma. But patients who undergo early diagnosis and phlebotomy treatment before the development of organ damage have a normal life expectancy. The haemochromatosis gene was recently isolated and encodes a HLA class I related protein. A missense mutation (C282Y) in the homozygous configuration was observed in more than 92% of the patients. So diagnosis and genetic counselling are getting modified by this direct genotyping test.

[Comparison of 2 methods of measuring microalbuminuria. Immunonephelometry and radioimmunology]. / Comparaison de deux méthodes de dosage de la microalbuminurie. L'immunonéphélémétrie et la radioimmunologie.

The early detection of microalbuminuria in insulin dependent diabetes is considered as a sign of initial stage of nephropathy (possibly reversible if glycemic balance is well maintained). This detection requires very accurate methods as radioimmunoassays. Yet, they are so slow that they represent an obstacle to systematic detection. We report an appraisement of an immunonephelemetric method. Results reveal that immunonephelemetry is a sensitive and accurate method (threshold of sensitivity 0.5 mg/l; CV intra assay less than 5%; CV inter assays less than 10%; analytical recovery: 94-104%). Moreover, immunonephelemetry and radioimmunology are significantly well correlated (r = 0.977, p less than 0.001). As a conclusion, we can say that thanks to complete automation, immunonephelemetry is a choice method to test great lines of samples.

[Molecular genetics of hemochromatosis]. / Génétique moléculaire de l'hémochromatose.

Hemochromatosis is a recessive disorder of iron metabolism characterized by progressive iron loading of parenchymal organs, which accounts for clinical complications such as cirrhosis, diabetes mellitus, cardiopathy, endocrine dysfunctions and arthropathy. Clinical complications, which usually develop after the third or fourth decade of life, can be fatal but may be prevented by phlebotomy if iron excess is detected at a very early stage. The hemochromatosis gene (HFE), located 4.5 megabases telomeric to the HLA-A locus, encodes an HLA class I like protein and two missense mutations, C282Y and H63D in complete disequilibrium have been identified within this gene. Due to its high frequency in the general population, the involvement of H63D in the pathogenesis of the disease remains controversial, and it might correspond to a minor mutation. Conversely, the C282Y mutation is tightly linked to the disease, as it accounts for 80 to 100% of the hemochromatosis cases in Northern Europe. The lower frequency observed, in the patients, in Italy and South of France led to imagine either the implication of other mutations or of other genes. The C282Y mutation is absent in Asia and Africa and is present in the general population with a decreasing gradient of frequency from Northern to Southern Europe. The prevalence of the disease was usually estimated to be 3% but the observed frequency of the C282Y homozygotes is 5% in our breton population raising the question of the penetrance of the disease, and consequently the use of the genotypic test for its systematic screening. As HFE encodes a membrane protein similar to HLA class I protein, its contribution to iron overload is not obvious. The normal protein is predicted to to be expressed at the cell surface in association with beta 2-microglobulin, a localization for which C282Y is critical as it disrupts this association. This protein has also been shown to form a stable complex with the transferrin receptor leading to a decreased affinity for transferrin. A better knowledge of its function will help to decipher iron and different metal-ions metabolism. Although the exact role of the HFE protein is unknown, the genotypic test allows the clinicians to ascertain their diagnosis and genetic counselling.

[The diagnosis of hemochromatosis in the era of the gene]. / Le diagnostic de l'hémochromatose à l'heure du gène.

The discovery of the hemochromatosis gene has deeply changed and simplified the diagnosis of the disease. In a given individual, establishing the diagnosis relies, from now on, on a simple blood sample showing the couple: elevated transferrin saturation and homozygous C282Y mutation (= C282Y +/+). Liver biopsy should only be performed when iron overload is massive in order to detect cirrhosis (or bridging fibrosis), i.e. in a prognostic view. Practically, liver biopsy is confined to the following two situations: when the C282Y +/+ patient exhibits hepatomegaly and/or an increase in serum transaminases and/or a serum ferritin level above 1,000 micrograms/L; whenever, despite a strong bio-clinical suspicion of iron overload, genetic testing does not show the expected homozygosity for C282Y. At the family level, evaluating the risk for hemochromatosis is now "instantaneous" thanks to genetic testing. One must, however, keep in mind in interpreting the data of the family members that: clinical expression of the homozygous status is not constant; heterozygosity for C282Y does not per se lead to significant iron overload, but may constitute a co-factor exacerbating (or increasing the risk of) other hepatic or non hepatic diseases. Heterozygosity exposes also to the risk of homozygosity among the offspring; this knowledge of C282Y status must be balanced by the negative impact from the standpoint of possible societal genetic discrimination.

[Molecular genetics of hemochromatosis]. / Génétique moléculaire de l'hémochromatose.

Haemochromatosis is an inherited disorder of iron metabolism characterized by a general iron over loading. Without diagnosis and early treatment, it is a serious and potentially fatal disease by cardiac failure or hepatocellular carcinoma in particular. Gene prevalence was estimated at 0.06 in Brittany, so that haemochromatosis may be the most common genetic disease in this area. The biochemical defect of the disease is unknown; only one fact is well established: the iron absorption through duodenal mucosa is excessive. However we don't know if it is a primary event. The gene is also unknown but in 1975 it was located on the short arm of chromosome 6, closely linked to the HLA class I region, less than 1 cM from HLA-A. None of the genes coding for the known iron proteins could be the haemochromatosis gene because of their chromosomal localization. In order to locate this gene with precision, we have used a reverse genetic approach now called positional cloning. Characterization of new polymorphic markers and linkage disequilibrium analysis, have led us to locate the gene within a 350 kb region around HLA-A. We have then searched for all the structural genes in this region. Seven new genes have been so identified and located with precision. A structural analysis of these genes was undertaken to find an eventual abnormality in patients.

Alpha-L-fucosidase in rat testis during sexual maturity.

alpha-L-fucosidase (EC 3.2.1.51) activity, concentration of testosterone (T), and its metabolite dihydrotestosterone (DHT) were tested in rat testis during the onset of puberty. This study was also carried out in testes of rats treated with 17-beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5-alpha-androstane-3-one (DMAA), an inhibitor of the 5-alpha-reductase-mediated conversion of T into DHT. alpha-L-fucosidase activity in seminiferous tubules of control and DMAA-treated rats was found to be relatively high on the 25th day after birth (approximately 24 units) but decreased and remained relatively constant the following days (approximately 10 units). In contrast, alpha-L-fucosidase activity was nearly undetectable in the immature interstitium of the control rats but sharply increased the following days. A maximum was reached at the 55th day, followed by a rapid decrease. alpha-L-fucosidase activity evolved in parallel with an increase and decrease of DHT concentration. In DMAA-treated rats with DHT levels and an alpha-L-fucosidase activity significantly lower than in the control rats between the 55th and the 65th days, this parallelism existed as well.

Non-C282Y familial iron overload: evidence for locus heterogeneity in haemochromatosis.

Haemochromatosis (HC) is an autosomal recessive disease with progressive iron overload leading to midlife onset of clinical complications. The causal gene (HFE) maps to 6p, in close linkage with the HLA class I genes. An HFE candidate gene recently identified has two missense mutations (C282Y and H63D) associated with the disease. Here we document the phenotypic and genetic analysis of a nuclear family comprising two sibs with symptomatic and massive iron overload before the age of 25. The disease seemed to be recessively transmitted and fitted the agreed criteria for haemochromatosis, but was neither associated with the C282Y and H63D mutations nor linked with HLA markers. Our data strongly support locus heterogeneity in haemochromatosis by showing evidence that the gene responsible for juvenile haemochromatosis (JH) does not map to 6p. In the absence of clear cut phenotypic distinction from typical haemochromatosis, patients below 30 years of age and C282Y negative should be considered as putative juvenile cases. This has practical implications in genetic counselling and family management.

A novel coding sequence belonging to a new multicopy gene family mapping within the human MHC class I region.

The human major histocompatibility complex (MHC) region is a genomic region spanning about 4000 kilobases (kb) including the class I, class II, and class III subregions. The class I subregion is larger than the two others but with fewer genes described to date. It includes a) classical human leucocyte antigen (HLA) class I genes (HLA-A, HLA-B, HLA-C) which are highly polymorphic and encode products presenting the endogenous antigenic peptides to the T-cell receptors, and b) non-classical class I genes (HLA-E, HLA-F, HLA-G) whose function is still unknown. In this study, we describe the first coding sequence which is not structurally related to the class I genes, although it is localized within the MHC class I region. This novel gene, P5-1, belongs to a multiple copy family, all members of which map within the MHC. Although the P5-1 sequence showed no similarity to sequences in different databanks, its transcription, which is restricted to lymphoid tissues, argues for an immunological function of its product.