8 - Classical and atypical HFE hemochromatosis

Summary

Hemochromatosis and HFE mutations

The “classical” type of familial hemochromatosis that is transmitted as an autosomal recessive disorder is usually due to homozygosity for the C282Y mutation of the HFE gene. It is expected that mutations of HFE cause the great majority of the cases of heritable iron overload in humans. There are at least 37 known mutations of the HFE gene (Table 8.1) (Chapter 4). Some individuals who are homozygous for any of the known mutations may develop heavy iron overload. At least six mutations are associated with mild iron accumulation; and at least six mutations were discovered in patients who did not have iron overload. There is insufficient reported information in the literature to determine if six of the mutations are sufficiently deleterious to result in iron overload. Approximately 1500 mutations of the cystic fibrosis gene (CF) are known, and the gene encodes a 1480 amino acid protein. In contrast, HFE is much smaller than CF, and encodes a protein of only 343 amino acids. Thus, it is expected that fewer mutations of HFE than mutations of CF will be eventually discovered.

Molecular genetics

Although the autosomal recessive inheritance pattern of “classical” hemochromatosis had long been recognized, identification of the responsible gene remained elusive for many years (Table 8.1). An important breakthrough in the search for the gene occurred in 1976 when hemochromatosis was found to be linked closely to the human leukocyte antigen (HLA)-A*03 region of the short arm of chromosome 6.