Acute intermittent porphyria (AIP)

Acute intermittent porphyria is a metabolic disorder of heme synthesis that manifests as erythrodontia, i.e. brown teeth that fluoresce pink under UV light, and reddish-brown urine.

Porphyrins are organic compounds that combine with iron to form heme. Heme is a component of many compounds (including hemoglobin, the oxygen-carrying molecule in the blood) that play a vital role in biological systems. The synthesis of heme is a complex multi-step process catalysed by several enzymes.  As to AIP, a deficiency of the enzyme hydroxymethylbilane synthase results in disruption of the normal heme synthesis pathway and accumulation of the intermediate porphyrins in teeth, bones and skin, leading to brown discoloration. Porphyrins are also excreted in the urine and faeces, causing a reddish-brown color of the urine. Some animals develop photosensitivity (sensitivity to the sun) and haemolytic anaemia due to a lack of circulating red blood cells

Several causative mutations in the HMBS gene have been identified so far. Genetic tests are available for mutations c.445C>T, c.826-1G>A, c.107_110del in domestic Shorthair cats and c.842_844del in Siamese cats. Genetic testing is generally recommended for all cats with brown-colored teeth and urine.

Inheritance of mutations is autosomal dominant. This means that it only takes one copy of the mutated gene inherited from either parent to cause symptoms of the disease. A genetic test can clearly reveal the genotype of an animal and is a useful tool for breeders to prevent unintentional breeding of affected individuals.

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References:

Clavero, S., Ahuja, Y., Bishop, D.F., Kwait, B., Haskins, M.E., Giger, U., Desnick, R.J. : Diagnosis of feline acute intermittent porphyria presenting with erythrodontia requires molecular analyses. Vet J 198:720-2, 2013. Pubmed reference: 24239138