Haemochromatosis in the new millennium.

Hereditary haemochromatosis (HHC) is a common inherited disorder of iron metabolism characterised by progressive iron loading of parenchymal cells of the liver, pancreas, heart and other organs ultimately leading to cirrhosis and organ failure. Despite HLA studies which localised the defective gene to the short arm of chromosome 6, the haemochromatosis gene remained elusive until 1996, when the gene was identified by a massive positional cloning effort. The haemochromatosis gene (HFE) encodes a novel nonclassical MHC class-1-like molecule. Two missense mutations have been identified in patients with HHC, a G to A at nucleotide 845, resulting in a substitution of tyrosine for cysteine at amino acid 282 (referred to as the C282Y mutation) and a C to G at nucleotide 187, resulting in a substitution of aspartate for histidine at amino acid 63 (H63D). An average of 85-90% of patients with typical clinical features of HHC are homozygous for the C282Y mutation. H63D is not associated with the same degree of iron loading as C282Y. Clinical expression is variable depending on environmental (dietary) iron, physiological and pathological blood loss and as yet unidentified modifying genetic factors. One recent Australian study indicates that only about 50% of homozygous subjects are fully expressing and symptomatic and that about 30% show no clinical or biochemical expression. Genetic tests for identifying mutations in the HFE gene provide precise means for diagnosis, family testing and population screening and have led to re-evaluation of the indications for liver biopsy in this disease. At the present time, however, the most practical and cost-effective method of screening is for phenotypic expression by transferrin saturation or unsaturated iron binding capacity measurement. In the future, population screening by genotype should be feasible once the relevant technical, legal and ethical issues are resolved.