HAMP and hemochromatosis type 1: Loss-of-function mutations in other genes encoding hepcidin (HAMP), hemojuvelin (HJV) and transferrin receptor 2 (TFR2) or gain-of-function mutations in the gene encoding ferroportin (SLC40A1) cause much rarer forms of hemochromatosis (non-HFE HH), but in general, iron accumulation proceeds at the higher rate, often leading to juvenile forms of the disease.