De Verneuil et al. (1978) classified porphyria cutanea tarda (PCT), the most common type of porphyria, into 2 types: type I, or 'sporadic' type, associated with approximately 50% level of uroporphyrinogen decarboxylase (UROD; 613521) in liver (Elder et al., 1978; Felsher et al., 1982), and type II, or 'familial' type (176100), characterized by 50% deficient activity of the same enzyme in many tissues (Kushner et al., 1976; Elder et al., 1980).
Type I is the most common form of PCT, comprising 70 to 80% of cases. The causes of the deficiency are often unclear and are probably multifactorial (review by Lambrecht et al., 2007). [from
OMIM]