Broadsheet number 54. Hereditary hemochromatosis

Human leukocyte antigen haplotypes and HFE mutations in Spanish hereditary hemochromatosis and sporadic porphyria cutanea tarda

BACKGROUND AND AIMS

It has been postulated that the HFE C282Y mutation (linked to human leukocyte antigen [HLA]-A3-B7 haplotype) is not only responsible for hereditary hemochromatosis; HLA class I alleles would also contribute to the disease pathogenesis. In addition, H63D mutation linked to HLA-A29-B44 would also be pathogenetic, particularly in the Mediterranean Basin and throughout the world. However, sporadic porphyria cutanea tarda (s-PCT) has also been linked to these HFE mutations. In the present work, we have studied HFE mutations and HLA genes to test these hypotheses.

METHODS

C282Y and H63D mutations together with HLA genetic typing have been performed in Spanish hereditary hemochromatosis (n = 98) and PCT (n = 63) patients. The etiologic fraction (delta) has been used to determine the absolute strongest gene linkage to both diseases.

RESULTS

The Spanish frequent HLA-A29-B44 haplotype is not significantly associated to the H63D mutations in hereditary hemochromatosis patients (although it is found more frequently in patients than in controls). Sporadic porphyria cutanea tarda patients do not show a significant association to H63D mutations, although it is also more frequent than in controls; however, compound H63D/C282Y subjects seem to bear a significant risk to s-PCT. Allelic C282Y (and not H63D) frequencies show a significant association with s-PCT.

CONCLUSIONS

The postulated additional risk of hereditary hemochromatosis given by class I HLA antigens may be secondary to the HFE gene linkage disequilibrium with certain class I alleles or to the existence of other neighboring genetic pathogenetic factors in our Spanish sample.

HFE mutation and dietary iron content interact to increase ischemia/reperfusion injury of the heart in mice

Hereditary hemochromatosis is an inherited pathological condition characterized by iron overload in several vital organs including heart. To increase our understanding of the underlying pathogenic mechanisms of hereditary hemochromatosis, we used a HFE gene knockout mouse model that replicates hereditary hemochromatosis. A group of mice with no copies of HFE gene and corresponding wild-type mice were maintained either on low-iron (30 ppm) or high-iron (300 ppm) diet since birth. The results of our study revealed that HFE gene knockout mouse hearts were susceptible to ischemia-reperfusion injury as evidenced by increased postischemic ventricular dysfunction, increased myocardial infarct size and cardiomyocyte apoptosis compared with wild-type control hearts. The degree of injury increased in the hearts of the mice fed high-iron diet. The hearts of the HFE knockout mice showed increased iron deposition, increased content of reactive oxygen species (ROS) as evidenced by the increased formation of malondialdehyde, and reduced antioxidant enzymes including superoxide dismutase, catalase, and glutathione peroxidase. The results suggest that increased amount of ROS and reduced antioxidant reserve secondary to iron overloading may be instrumental for the susceptibility of the HFE gene knockout mice to cardiac injury.

Mouse strain differences determine severity of iron accumulation in Hfe knockout model of hereditary hemochromatosis

Hereditary hemochromatosis (HH) is a common disorder of iron metabolism caused by mutation in HFE, a gene encoding an MHC class I-like protein. Clinical studies demonstrate that the severity of iron loading is highly variable among individuals with identical HFE genotypes. To determine whether genetic factors other than Hfe genotype influence the severity of iron loading in the murine model of HH, we bred the disrupted murine Hfe allele onto three different genetically defined mouse strains (AKR, C57BL/6, and C3H), which differ in basal iron status and sensitivity to dietary iron loading. Serum transferrin saturations (percent saturation of serum transferrin with iron), hepatic and splenic iron concentrations, and hepatocellular iron distribution patterns were compared for wild-type (Hfe +/+), heterozygote (Hfe +/-), and knockout (Hfe -/-) mice from each strain. Although the Hfe -/- mice from all three strains demonstrated increased transferrin saturations and liver iron concentrations compared with Hfe +/+ mice, strain differences in severity of iron accumulation were striking. Targeted disruption of the Hfe gene led to hepatic iron levels in Hfe -/- AKR mice that were 2.5 or 3.6 times higher than those of Hfe -/- C3H or Hfe -/- C57BL/6 mice, respectively. The Hfe -/- mice also demonstrated strain-dependent differences in transferrin saturation, with the highest values in AKR mice and the lowest values in C3H mice. These observations demonstrate that heritable factors markedly influence iron homeostasis in response to Hfe disruption. Analysis of mice from crosses between C57BL/6 and AKR mice should allow the mapping and subsequent identification of genes modifying the severity of iron loading in this murine model of HH.

Hemochromatosis: diagnosis and management

HH should be distinguished from the other syndromes of iron overload. Many patients with HH have abnormal serum iron values before the development of any significant symptoms or clinical findings, and liver biopsy is less important in these patients. HFE mutation analysis has strengthened our ability to diagnose HH accurately and is useful in family studies. HFE mutations may play a contributory role in some patients with PCT, NASH, or chronic HCV. Generalized population screening for HH may someday become a reality and lead to the identification and treatment of more patients before they have tissue damage or increased morbidity. With the identification of the HFE gene, we are beginning to unravel many of the mysteries of both normal iron absorption and the disorder of iron metabolism found in patients with HH.