The 16189 variant of mitochondrial DNA occurs more frequently in C282Y homozygotes with haemochromatosis than those without iron loading.
ABSTRACT: 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.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.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).Iron loading in C282Y homozygotes with HH was exacerbated by the presence of the mitochondrial 16189 variant.
Project description:Genetic testing can determine those at risk for hereditary haemochromatosis (HH) caused by HFE mutations before the onset of symptoms. However, there is no optimum screening strategy, mainly owing to the variable penetrance in those who are homozygous for the HFE Cys282Tyr (C282Y) mutation. The objective of this study was to identify the majority of individuals at serious risk of developing HFE haemochromatosis before they developed life threatening complications.We first estimated the therapeutic penetrance of the C282Y mutation in people living in la Somme, France, using genetic, demographic, biochemical, and follow up data. We examined the benefits of neonatal screening on the basis of increased risk to relatives of newborns carrying one or two copies of the C282Y mutation. Between 1999 and 2002, we screened 7038 newborns from two maternity hospitals in the north of France for the C282Y and His63Asp (H63D) mutations in the HFE gene, using bloodspots collected on Guthrie cards. Family studies and genetic counselling were undertaken, based on the results of the baby's genotype.In la Somme, we found that 24% of the adults homozygous for the C282Y mutation required at least 5 g iron to be removed to restore normal iron parameters (that is, the therapeutic penetrance). In the reverse cascade screening study, we identified 19 C282Y homozygotes (1/370), 491 heterozygotes (1/14) and 166 compound heterozygotes (1/42) in 7038 newborns tested. The reverse cascade screening strategy resulted in 80 adults being screened for both mutations. We identified 10 previously unknown C282Y homozygotes of whom six (four men and two women) required venesection. Acceptance of neonatal screening was high; parents understood the risks of having HH and the benefits of early detection, but a number of parents were reluctant to take the test themselves. Neonatal screening for HH is straightforward. Reverse cascade screening increased the efficiency of detecting affected adults with undiagnosed haemochromatosis. This strategy allows almost complete coverage for HH and could be a model for efficient screening for other late onset genetic diseases.
Project description:BACKGROUND: Haemochromatosis is associated with mutations in the HFE gene but the significance of these mutations in the general population is unknown. AIMS: To determine the frequency of HFE gene mutations in the general population, their effect on serum iron indexes, and their role in screening for haemochromatosis. METHODS: Deoxyribonucleic acid (DNA) from 1064 randomly selected subjects was analysed for the C282Y and H63D mutations in the HFE gene. Serum iron, transferrin saturation, and ferritin were measured and individuals with increased iron indexes were investigated to confirm or exclude a clinical diagnosis of haemochromatosis. RESULTS: Mutations were identified in 409 individuals (38.4%) with heterozygote (carrier) frequencies of 13.2% and 24.3% for the C282Y and H63D mutations respectively. Heterozygosity for either mutation significantly increased serum iron and transferrin saturation but despite a similar trend for ferritin, this was only significant for C282Y homozygotes. Five individuals (0.47%) were homozygous for the C282Y mutation, three of whom had haemochromatosis confirmed by liver biopsy (0.28%). The other two C282Y homozygotes would not have been detected by phenotypic screening alone. CONCLUSIONS: HFE mutations are present in 38.4% of the population, affect serum iron indexes, and are important determinants of iron status. The population frequency of genetically defined haemochromatosis (C282Y homozygosity) is approximately one in 200 and is higher than the prevalence of clinically apparent haemochromatosis.
Project description:To test the hypothesis that differences in duodenal iron absorption may explain the variable phenotypic expression among HFE C282Y homozygotes, we have compared relative gene expression of duodenal iron transporters among C282Y homozygotes [hereditary hemochromatosis (HH)] with and without iron overload. Duodenal biopsy samples were analyzed using real-time PCR for expression of DMT1, FPN1, DCYTB, and HEPH relative to GAPDH from 23 C282Y homozygotes, including 5 "nonexpressors" (serum ferritin < upper limit of normal and absence of phenotypic features of hemochromatosis) and 18 "expressors." Four subjects of wild type for HFE mutations without iron overload or liver disease served as controls. There was a significant difference in expression of DMT1 (P = 0.03) and DMT1(IRE) (P = 0.0013) but not FPN1, DCYTB, or HEPH between groups. Expression of DMT1(IRE) was increased among HH subjects after phlebotomy compared with untreated (P = 0.006) and nonexpressor groups (P = 0.026). A positive relationship was observed among all HH subjects regardless of phenotype or treatment status between relative expression of FPN1 and DMT1 (r = 0.5854, P = 0.0021), FPN1, and DCYTB (r = 0.5554, P = 0.0040), FPN1 and HEPH (r = 0.5100, P = 0.0092), and DCYTB and HEPH (r = 0.5400, P = 0.0053). In summary, phlebotomy is associated with upregulation of DMT1(IRE) expression in HH subjects. HFE C282Y homozygotes without phenotypic expression do not have significantly decreased duodenal gene expression of iron transport genes compared with HH subjects with iron overload. There is coordinated regulation between duodenal expression of FPN1 and DMT1, FPN1 and DCYTB, and FPN1 and HEPH and also DCYTB and HEPH in HH subjects regardless of phenotype.
Project description:Hepatic siderosis is common in patients with porphyria cutanea tarda (PCT). Mutations in the hereditary hemochromatosis (hh) gene (HFE) explain the siderosis in approximately 20% patients, suggesting that the remaining occurrences result from additional genetic and environmental factors. Two genes known to modify iron loading in hh are hepcidin (HAMP) and hemojuvelin (HJV). To determine if mutations in or expression of these genes influenced iron overload in PCT, we compared sequences of HAMP and HJV in 96 patients with PCT and 88 HFE C282Y homozygotes with marked hepatic iron overload. We also compared hepatic expression of these and other iron-related genes in a group of patients with PCT and hh. Two intronic polymorphisms in HJV were associated with elevated serum ferritin in HFE C282Y homozygotes. No exonic polymorphisms were identified. Sequencing of HAMP revealed exonic polymorphisms in 2 patients with PCT: heterozygosity for a G-->A transition (G71D substitution) in one and heterozygosity for an A-->G transition (K83R substitution) in the other. Hepatic HAMP expression in patients with PCT was significantly reduced, regardless of HFE genotype, when compared with patients with hh but without PCT with comparable iron overload. These data indicate that the hepatic siderosis associated with PCT likely results from dysregulated HAMP.
Project description:We observed the development of phenotypic hereditary haemochromatosis in a non-hereditary haemochromatosis liver transplant recipient, following transplantation with a liver from a C282Y heterozygous donor. No cause for secondary iron overload was identified. Subsequent sequencing of the HFE gene of both donor and recipient revealed a strong candidate for a novel pathogenic HFE mutation. In the recipient, heterozygosity for a single base substitution in exon 1, g.18 G>C, resulting in the substitution of arginine by serine at codon 6 (R6S), was detected. This R6S variation is likely to represent a novel pathogenic missense mutation of the HFE gene. An interaction between R6S heterozygosity in the recipient and C282Y heterozygosity in the donor liver is the most likely explanation for the development of iron overload in this patient. The report suggests that an hepatic defect is required for expression of hereditary haemochromatosis and that the intestinal HFE genotype is not the exclusive determinant of iron status. It also raises the possibility that a hereditary haemochromatosis phenotype may result from transplantation of C282Y heterozygous donor livers into recipients with heterozygous pathogenic HFE mutations. This possibility may have significant implications for the common practice of transplanting C282Y heterozygous livers.
Project description:Beta2-microglobulin was investigated in atypical haemochromatosis patients not homozygous for the C282Y mutation of HFE (OMIM *235200), because the HFE protein binds beta2-microglobulin, and in mice beta2-microglobulin gene knockout causes hepatic iron overload. Six unrelated patients with atypical haemochromatosis were studied. Five patients had normal HFE coding sequence and the sixth was heterozygous for C282Y. We show that the spectrum of atypical haemochromatosis includes two distinct familial forms: juvenile haemochromatosis (OMIM *602390) and a novel form of familial iron overload, with apparently autosomal dominant inheritance, predominant Kupffer cell siderosis, and possible minimal dyserythropoiesis on bone marrow examination. Serial serum beta2-microglobulin estimation showed normal levels in all patients. Southern blot analysis showed normal beta2-microglobulin gene structure, excluding major gene rearrangement. Several corrections to the published beta2-microglobulin sequence were identified, but all six patients had normal beta2-microglobulin sequence. Western blot analysis of serum showed beta2-microglobulin protein of normal size. In conclusion, we found no evidence to implicate beta2-microglobulin mutation in atypical haemochromatosis. Two forms of familial iron overload appear unrelated to either HFE or beta2-microglobulin. Linkage studies are required to identify the genes involved, which may encode novel proteins crucial to the regulation of iron metabolism. Identification of these loci will aid the diagnosis, counselling, and treatment of iron overload disorders.
Project description:Haemochromatosis is defined as systemic iron overload of genetic origin, caused by a reduction in the concentration of the iron regulatory hormone hepcidin, or a reduction in hepcidin-ferroportin binding. Hepcidin regulates the activity of ferroportin, which is the only identified cellular iron exporter. The most common form of haemochromatosis is due to homozygous mutations (specifically, the C282Y mutation) in HFE, which encodes hereditary haemochromatosis protein. Non-HFE forms of haemochromatosis due to mutations in HAMP, HJV or TFR2 are much rarer. Mutations in SLC40A1 (also known as FPN1; encoding ferroportin) that prevent hepcidin-ferroportin binding also cause haemochromatosis. Cellular iron excess in HFE and non-HFE forms of haemochromatosis is caused by increased concentrations of plasma iron, which can lead to the accumulation of iron in parenchymal cells, particularly hepatocytes, pancreatic cells and cardiomyocytes. Diagnosis is noninvasive and includes clinical examination, assessment of plasma iron parameters, imaging and genetic testing. The mainstay therapy is phlebotomy, although iron chelation can be used in some patients. Hepcidin supplementation might be an innovative future approach.
Project description:Both familial and sporadic porphyria cutanea tarda (PCT) are iron dependent diseases. Symptoms of PCT resolve when iron stores are depleted by phlebotomy, and a sequence variant of HFE (C282Y, c.843G>A, rs1800562) that enhances iron aborption by reducing hepcidin expression is a risk factor for PCT. Recently, a polymorphic variant (D519G, c.1556A>G, rs11558492) of glyceronephosphate O-acyltransferase (GNPAT) was shown to be enriched in male patients with type I hereditary hemochromatosis (HFE C282Y homozygotes) who presented with a high iron phenotype, suggesting that GNPAT D519G, like HFE C282Y, is a modifier of iron homeostasis that favors iron absorption. To challenge this hypothesis, we investigated the frequency of GNPAT D519G in patients with both familial and sporadic PCT. Patients were screened for GNPAT D519G and allelic variants of HFE (both C282Y and H63D). Nucleotide sequencing of uroporphyrinogen decarboxylase (URO-D) identified mutant alleles. Patients with low erythrocyte URO-D activity or a damaging URO-D variant were classified as familial PCT (fPCT) and those with wild-type URO-D were classified as sporadic PCT (sPCT). GNPAT D519G was significantly enriched in the fPCT patient population (p = 0.0014) but not in the sPCT population (p = 0.4477). Both HFE C282Y and H63D (c.187C>G, rs1799945) were enriched in both PCT patient populations (p<0.0001) but showed no greater association with fPCT than with sPCT.GNPAT D519G is a risk factor for fPCT, but not for sPCT.
Project description:Relationships of thyroid and iron measures in large cohorts are unreported. We evaluated thyroid-stimulating hormone (TSH) and free thyroxine (T4) in white participants of the primary care-based Hemochromatosis and Iron Overload Screening (HEIRS) Study.We measured serum TSH and free T4 in 176 HFE C282Y homozygotes without previous hemochromatosis diagnoses and in 312 controls without HFE C282Y or H63D who had normal serum iron measures and were matched to C282Y homozygotes for Field Center, age group, and initial screening date. We defined hypothyroidism as having TSH >5.00 mIU/L and free T4 <0.70 ng/dL, and hyperthyroidism as having TSH <0.400 mIU/L and free T4 >1.85 ng/dL. Multivariate analyses were performed using age, sex, Field Center, log(10) serum ferritin (SF), HFE genotype, log(10) TSH, and log(10) free T4.Prevalences of hypothyroidism in C282Y homozygotes and controls were 1.7% and 1.3%, respectively, and of hyperthyroidism 0% and 1.0%, respectively. Corresponding prevalences did not differ significantly. Correlations of log(10) SF with log(10) free T4 were positive (p = 0.2368, C282Y homozygotes; p = 0.0492, controls). Independent predictors of log(10) free T4 were log(10) TSH (negative association) and age (positive association); positive predictors of log(10) SF were age, male sex, and C282Y homozygosity. Proportions of C282Y homozygotes and controls who took medications to supplement or suppress thyroid function did not differ significantly.Prevalences of hypothyroidism and hyperthyroidism are similar in C282Y homozygotes without previous hemochromatosis diagnoses and controls. In controls, there is a significant positive association of SF with free T4. We conclude that there is no rationale for routine measurement of TSH or free T4 levels in hemochromatosis or iron overload screening programs.
Project description:HFE, an atypical MHC class I type molecule, has a critical, yet still elusive function in the regulation of systemic iron metabolism. HFE mutations are linked to hereditary haemochromatosis type 1, a common autosomal recessive disorder of iron overload. Most patients are homozygous for a C282Y point mutation that abrogates the interaction of HFE with beta(2)-microglobulin (beta(2)M) and, thus, impairs its proper processing and expression on the cell surface. An H63D substitution is also associated with disease. To investigate the function of HFE we have generated clones of human H1299 lung cancer cells that express wild-type, C282Y or H63D HFE under the control of a tetracycline-inducible promoter. Consistent with earlier observations in other cell lines, the expression of wild-type or H63D, but not C282Y, HFE induces an apparent iron-deficient phenotype, manifested in the activation of iron-regulatory protein and concomitant increase in transferrin receptor levels and decrease in ferritin content. This phenotype persists in cells expressing wild-type HFE after transfection with a beta(2)M cDNA. Whereas endogenous beta(2)M is sufficient for the presentation of at least a fraction of chimeric HFE on the cell surface, this effect is stimulated by approx. 2.8-fold in beta(2)M transfectants. The co-expression of exogenous beta(2)M does not significantly affect the half-life of HFE. These results suggest that the apparent iron-deficient phenotype elicited by HFE is not linked to beta(2)M insufficiency.