[Hemochromatosis: the most common of rare diseases].

Familial (hereditary) haemochromatosis (HH) is an iron storage disorder characterized by an increased intestinal absorption of iron and its accumulation in numerous tissues. The disease generates an iron overload with tissue damages also seen in haematologic disturbances (with dyserythropoiesis and haemolysis) and hepatic disorders. Besides typical mutations linked to HH (C282 Y and H63D, HFE locus), three other mutations have been identified and more have to be defined. A complete genetic testing is important to assess the risk of morbidity. Indeed, the clinical picture of HH is dependent upon the specific mutations as well as the individual context (sex, environment, associated hepatic and/or haematologic disorders). Porphyria cutanea tarda (PCT) has for long been found significantly associated with HH. It is now considered that hepatic iron overload related to the combination of heterogeneous genetic traits and environmental factors, including alcoholism and viral hepatitis, precipitates the expression of PCT through the inhibition of uroporphyrinogen decarboxylase (Uro.D).