Cells which synthesize heme are predominantly erythroblasts/reticulocytes in the bone marrow (80%) and hepatocytes (20%). Deficiency of FECH results in increased release of<unk> , which binds to albumin in plasma and subsequently undergoes hepatic extraction. Normally, most<unk>  in hepatocytes is secreted into bile; the remainder undergoes transformation into heme. Some<unk>  in bile is returned to the liver as a consequence of the enterohepatic circulation; the remaining<unk>  in the intestine undergoes fecal excretion.<unk>  is insoluble and hence unavailable for renal excretion. In<unk> , subnormal biotransformation of<unk>  into heme results in accumulation of<unk>  in hepatocytes. Since FECH deficiency is associated with increased concentrations of<unk>  in erythrocytes, plasma, skin and liver, retention of<unk>  in skin predisposes to acute photosensitivity. As a result of absorption of ultraviolet and visible light (peak sensitivity at 400 nm, with lesser peaks between 500-625 nm) by<unk>  in plasma and erythrocytes when blood circulates through the dermal vessels, free radicals are formed, erythrocytes become unstable and injury to the skin is induced. A significant increase in the hepatobiliary excretion of<unk>  can damage the liver through both cholestatic phenomena and oxidative stress - predisposing to hepatobiliary disease of varying degrees of severity
Erythropoietic protoporphyria
Xeroderma pigmentosum
Pseudoporphyria
Harderoporphyria
Thalassemia
Scurvy
Hemoglobinemia
Megavitamin-B6 syndrome