endocrine and metabolic disorders
Overview of Porphyrias
Etiology of Porphyrias
With the exception of the sporadic type of Porphyria Cutanea Tarda (PCT, which also has an inherited type), the porphyrias are inherited diseases. Autosomal dominant inheritance is most common. In theautosomal dominant porphyrias, homozygous or compound heterozygous states (ie, 2 separate heterozygous mutations, one in each allele of the same gene in the same patient) may be incompatible with life, typically causing fetal death. Disease penetrance in heterozygotes varies; thus, clinically expressed disease is less common than genetic prevalence. Of the 2 most common porphyrias, acute intermittent porphyria (AIP) is autosomal dominant and about 20% of PCT cases are autosomal dominant. The prevalence of PCT is about 1/10,000. The prevalence of the causative genetic mutation for AIP is about 1/1500, but because penetrance is low, the prevalence of clinical disease is also about 1/10,000. Prevalence of both PCT and AIP varies widely among regions and ethnic groups. , only homozygous or compound heterozygous states cause disease. Erythropoietic Protoporphyria and X-linked Protoporphyria , the 3rd most common porphyria, is autosomal recessive. X-linked inheritance occurs in one of the porphyrias, Erythropoietic Protoporphyria and X-linked Protoporphyria . 