Natural history of hemochromatosis

Haemochromatosis

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.

HFE p.C282Y homozygosity predisposes to rapid serum ferritin rise after menopause: A genotype-stratified cohort study of hemochromatosis in Australian women

BACKGROUND AND AIM

Women who are homozygous for the p.C282Y mutation in the HFE gene are at much lower risk of iron overload-related disease than p.C282Y homozygous men, presumably because of the iron-depleting effects of menstruation and pregnancy. We used data from a population cohort study to model the impact of menstruation cessation at menopause on serum ferritin (SF) levels in female p.C282Y homozygotes, with p.C282Y/p.H63D simple or compound heterozygotes and those with neither p.C282Y nor p.H63D mutations (HFE wild types) as comparison groups.

METHODS

A sample of the Melbourne Collaborative Cohort Study was selected for the "HealthIron" study (n = 1438) including all HFE p.C282Y homozygotes plus a random sample stratified by HFE-genotype (p.C282Y and p.H63D). The relationship between the natural logarithm of SF and time since menopause was examined using linear mixed models incorporating spline smoothing.

RESULTS

For p.C282Y homozygotes, SF increased by a factor of 3.6 (95% CI (1.8, 7.0), P < 0.001) during the first 10 years postmenopause, after which SF continued to increase but at less than half the previous rate. In contrast, SF profiles for other HFE genotype groups increase more gradually and did not show a distinction between premenopausal and postmenopausal SF levels. Only p.C282Y homozygotes had predicted SF exceeding 200 μg/L postmenopause, but the projected SF did not increase the risk of iron overload-related disease.

CONCLUSIONS

These data provide the first documented evidence that physiological blood loss is a major factor in determining the marked gender difference in expression of p.C282Y homozygosity.

Hereditary hemochromatosis: pathophysiology, diagnosis, and management

Hereditary hemochromatosis (HH) is an autosomal recessive genetic disease resulting in inappropriate intestinal iron absorption leading to iron overload and end-organ disease. The disease is most prevalent in white individuals of European descent. The C282Y mutation on the HFE gene accounts for most cases of HH; however, other genetic mutations have been identified. End-organ damage results in cirrhosis, diabetes mellitus, and cardiomyopathy. Therapeutic phlebotomy to deplete excessive iron stores is the standard treatment of HH and results in normal longevity if therapy is initiated before end-organ disease occurs.

Haemochromatosis

Since the discovery of the haemochromatosis gene (HFE; chromosome 6p21.3) associated with haemochromatosis in 1996, many studies about diverse aspects of this common genetic disorder have been done. Some patients present with cirrhosis and show high mortality, whereas many asymptomatic homozygotes for the C282Y mutation in the haemochromatosis gene identified in population screening studies, who have been followed up for many years, do not develop iron overload. Studies described the usefulness of transferrin saturation and serum ferritin tests, and the acceptability of genetic testing for haemochromatosis. Phlebotomy therapy improves hepatic fibrosis. Here, we summarise some new findings in haemochromatosis, a disorder first described in 1865.

Iron storage disease: facts, fiction and progress

There are many forms of iron storage disease, some hereditary and some acquired. The most common of the hereditary forms is HFE-associated hemochromatosis, and it is this disorder that is the main focus of this presentation. The body iron content is regulated by controlling absorption, and studies in the past decade have clarified, in part, how this regulation functions. A 25-amino-acid peptide hepcidin is up-regulated by iron and by inflammation, and it inhibits iron absorption and traps iron in macrophages by binding to and causing degradation of the iron transport protein ferroportin. Most forms of hemochromatosis results from dysregulation of hepcidin or defects of hepcidin or ferroportin themselves. Hereditary hemochromatosis was once considered to be very rare, but in the 1970s and 1980s, with the introduction of better diagnostic tests, it was considered the most common disease among Europeans. Controlled epidemiologic studies carried out in the last decade have shown, however, the disease itself actually is rare, and only its genotype and associated biochemical changes that are common. We do not understand why only a few homozygotes develop severe disease. It now seems unlikely that there are important modifying genes, and although alcohol is known to have some effect, excess drinking probably plays only a modest role in determining the hemochromatosis phenotype. Hereditary hemochromatosis is readily treated by phlebotomy. Secondary forms of the disease require chelation therapy, and the recent introduction of effective oral chelating agents is an important step forward in treating patients with disorders in which iron overload often proves to be fatal, such as thalassemia, myelodysplastic anemias, and dyserythropoietic anemias. While much has been learned about the regulation of iron homeostasis in the past decade, many mysteries remain and represent challenges that will keep us occupied for years to come.

Review article: the modern diagnosis and management of haemochromatosis

Haemochromatosis is the most common genetic disease in populations of European ancestry. Despite estimates based on genetic testing in Caucasian populations of 1 in 227, many physicians consider haemochromatosis to be a rare disease. The diagnosis can be elusive because of the non-specific nature of the symptoms. Of all the symptoms, liver disease has the most consistent relationship to haemochromatosis and the prognosis of haemochromatosis is most closely linked to the degree of iron overload. With the discovery of the HFE gene in 1996, comes new insights into the pathogenesis of the disease and new diagnostic strategies. However, a growing number of new iron-related genes have been discovered and linked to other iron overload syndromes.

Prevalence of Three Hereditary Hemochromatosis Mutant Alleles in the Michigan Caucasian Population

OBJECTIVE

To investigate the prevalence in the Michigan non-Hispanic Caucasian population of the C282Y, H63D and S65C mutations in the HFE gene associated with hereditary hemochromatosis.

METHODS

Polymerase chain reaction and restriction fragment length polymorphism analysis were performed on 3,532 blood samples from newborn screening cards provided by the state of Michigan.

RESULTS

More than 30% of Michigan Caucasians carry one HFE mutation, while 6% have two mutations. The allele frequency of the C282Y mutation is 5.7%, significantly higher than expected (p < 0.05), while the frequency of the H63D mutation is 14%, significantly lower than expected (p < 0.01).

CONCLUSIONS

This is the first publication to examine HFE allele frequencies in an unbiased sample of the Caucasian population. Results indicate that the C282Y mutation may be more common in the non-Hispanic Caucasian population than previously reported, and medical problems related to iron overload may be a health concern for Michigan non-Hispanic Caucasians. Additional studies of penetrance for the C282Y allele are required to fully understand the impact of this information.

Haemochromatosis: find them or forget about them?

Haemochromatosis continues to be considered an uncommon disease despite large scale population screening studies demonstrating a high prevalence of C282Y homozygotes of approximately 1 in 200. Since many of the C282Y homozygotes that are discovered through screening are asymptomatic, or have non-specific symptoms commonly found in the ageing population, the attribution of any symptoms to haemochromatosis has become increasingly difficult. The demonstration of significant liver disease in family members is a strong reminder of the vital importance of pedigree studies when a typical haemochromatosis patient is identified.