Acute intermittent porphyria is a autosomal dominant disorder caused by a defect in porphobilinogen deaminase activity. If peripheral neuropathy, such as pain in the back and legs or parathesias occurs it is almost always preceded by abdominal pain. The defect in porphobilinogen deaminase causes a build up of ALA and porphobilinogen (PBG) which causes their increased secretion in the urine.

Urine PBG is raised in acute intermittent porphyria, and the urine typically turns a red brown/ red colour on standing.