Porphyria cutanea tarda

Poryhyria cutanea tarda (PCT) is a skin disease that results front decrease d activity of uroporphyrinogen decarboxylase (UROD). About 80% of patients have the sporadic (type I) form in which UROD deficiency is restricted to t he liver. Others have familial (type II) PCT in which mutations in the UROD gene are inherited in an autosomal dominant pattern with low clinical pene trance. PCT may also follow exposure to porphyrogenic chemicals. Clinically overt PCT (types I and II) is provoked by liver cell injury, particularly when associated with alcohol abuse, hepatitis C infection, or estrogens. He patic iron overload is common, depletion of iron stores produces remission, and their replenishment lends to relapse. In PCT, hepatic UROD is inactiva ted by a process targeted at its catalytic sire, which is iron-dependent, r equires a heme precursor; and may be accelerated by induction of cytochrome P450s. Susceptibility to develop PCT in response to common causes of liver injury may be determined by co-inheritance of genes that regulate componen ts of this inactivation process.