Acute intermittent porphyria

Question 1

Pathology

Genetics

Answer 1

Acute intermittent porphyria (AIP) is a rare autosomal dominant condition caused by a defect in porphobilinogen deaminase, an enzyme involved in the biosynthesis of haem.

The results in the toxic accumulation of delta aminolaevulinic acid and porphobilinogen.

Question 2

Clinical Features

Answer 2

It characteristically presents with abdominal and neuropsychiatric symptoms in 20-40 year olds. AIP is more common in females (5:1)

• abdominal: abdominal pain, vomiting
• neurological: motor neuropathy
• psychiatric: e.g. depression
• hypertension and tachycardia common

Question 3

Diagnosis

Answer 3

classically urine turns deep red on standing

raised urinary porphobilinogen (elevated between attacks and to a greater extent during acute attacks)

assay of red cells for porphobilinogen deaminase

raised serum levels of delta aminolaevulinic acid and porphobilinogen

Question 4

Triggers of acute porphyrias

Answer 4

The acute porphyrias are triggered by:

Antibiotics - Rifampicin, Isoniazid, Nitrofurantoin
Anaesthetic agents - Ketamine, Etomidate
Sulfonamides
Barbiturates
Antifungal agents

Question 5

Management

Answer 5

Haem arginate can also be given intravenously to replenish haem levels.