Acute Porphyria – Classification

Acute porphyrias viewed from perspective of heme biosynthesis pathway. The enzyme involved at each step is listed on the left, and the type of porphyria associated with a deficiency of each enzyme is shown on the right. Acute porphyrias are highlighted in red. AIP, HCP and VP are autosomal dominant inherited diseases whereas ADP is autosomal recessive. Consistent with autosomal dominant inheritance, enzyme activities in AIP, HCP and VP are reduced to about 50% of normal. They are much lower in ADP, in which both alleles are mutated. Only a small fraction of individuals who inherit AIP, HCP and VP have clinical manifestations, indicating the importance of environmental triggers and/or genetic modifiers. Porphyric attacks, when they occur, can be severe and life threatening. They typically consist of acute neurovisceral attacks, identical in all three conditions. VP and to a lesser extent HCP, but not AIP, may also be associated with bullous skin lesions that occur in absence or presence of acute attacks. Acute attacks are rare before puberty and often provoked by identifiable precipitants, notably certain drugs, endocrine factors and alcohol. ADP is the rarest type of porphyria, with only six documented cases reported worldwide. Learn more here.

Prevalence of acute porphyria

Of the 4 acute porphyrias, acute intermittent porphyria (AIP) is the most common type of acute porphyria worldwide with estimated prevalence in the US of 5 per 100,000 persons.

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