Acute intermittent porphyria

Acute intermittent porphyria (AIP) is a rare metabolic disorder affecting the production of heme resulting from a deficiency of the enzyme porphobilinogen deaminase. It is the most common of the acute porphyrias. The clinical presentation of AIP is highly variable and non-specific. The patients are typically asymptomatic, with most gene carriers having no family history because the condition had remained latent for several generations. The syndrome marked by acute attacks affects only 10% of gene carriers. The mean age at diagnosis is 33 years old. Like other porphyrias, AIP is more likely to present in women. A distinguishing feature of AIP that separates it from other porphyrias is the absence of photosensitive cutaneous symptoms that occur in addition to acute attacks. AIP is one of the four porphyrias that presents as an acute attack. 90% of affected individuals never experience an acute attack and are asymptomatic, while an estimated 5% of affected individuals experience repeat attacks. Attacks are most common in young adult women and are rare before puberty or after menopause. Severe acute attacks may require hospitalization. Patients usually experience symptoms in attacks that last from several hours to a few days. Between attacks, patients are asymptomatic. The most frequent presenting symptoms are abdominal pain and tachycardia. The abdominal pain is typically severe, colicky, poorly localized, and often associated with pain in back and legs. Patients may also present with vomiting and constipation, but diarrhea is unusual. The onset of back and leg pain is characterized by severe pain and stiffness in back and thighs followed by loss of tendon reflexes and paralysis. Psychiatric symptoms are present, such as paranoid schizophrenia-like features but rarely psychosis and hallucinations. The acute attacks classically present with dark-red photosensitive urine (often called port-wine urine), but this is a nonspecific symptom. Physical examination often shows no abnormalities.