Acute intermittent porphyria (AIP) is the most common of the acute porphyrias and has a female predominance. It is an autosomal dominant genetic disease marked by deficient levels of the enzyme porphobilinogen deaminase. AIP is caused by a mutation on gene HMBS, which has the ability to result in a buildup of porphyrin.

This underlying deficiency must be combined with a trigger in order to produce symptoms. Triggers include certain drugs (porphyrinogenic), alcohol consumption, cigarette or marijuana smoking, stress, infections, fasting, or diet changes.

Patients usually experience symptoms in attacks that last from several hours to a few days. Severe acute attacks may require hospitalization. Between attacks, patients are asymptomatic.

Presentation is highly variable. Findings include abdominal pain, nausea / vomiting, constipation, tachycardia, weak extremities, urinary retention, dark urine (purple, red, brown, port-wine-colored), mental status changes, convulsions, hyponatremia, and peripheral neuropathy that may progress to respiratory paralysis. One theory behind neurologic dysfunction is that one or more of the heme pathway intermediates are neurotoxic. During attacks, urinary aminolevulinic acid (ALA) and porphobilinogen levels increase.