Primary or idiopathic hemochromatosis occurs no more than once in 10,000 births and probably develops only in individuals who are homozygous for a pair of abnormal autosomal genes. Secondary hemochromatosis is a much more common disorder that develops in heterozygous carriers of one such abnormal gene whose livers have been damaged exogenously, generally by alcohol. The precise chemical effect of one, or a pair, of these "hemochromatosis genes," in producing abnormally high iron retention, is unknown. This has made it impossible to diagnose the illness except on the basis of family history, the clinical picture, and several abnormalities of iron metabolism.
Scheinberg IH. The Genetics of Hemochromatosis. Arch Intern Med. 1973;132(1):126-128. doi:10.1001/archinte.1973.03650070112019