Acute Intermittent Porphyria (Variant 5)

Acute intermittent porphyria (AIP) is an inherited disorder affecting heme group synthesis, characterized by brown teeth and brown urine due to the accumulation of porphyrins. This condition is caused by mutations in the hydroxymethylbilane synthase (HMBS) gene, resulting in reduced enzyme activity in the heme group synthesis pathway.

Symptoms

Intermittent water porphyria includes clinical signs such as erythrodontia (brown teeth), brown urine and bones, which fluoresce under ultraviolet light. Affected cats may have low hemoglobin and iron levels, as well as decreased hematocrit and mean corpuscular volume. The activity of hydroxymethylbilane synthase (HMB), responsible for the synthesis of the heme group, is reduced by half and urine levels of aminolevulinic acid (ALA), porphobilinogen (PBG), uroporphyrin and coproporphyrin are elevated.

Disease Management

Disease management focuses on reducing triggers and controlling acute symptoms. It is essential to avoid stress and any agent that may induce HMB synthase enzyme activity, such as certain medications, foods or environmental changes. Administration of hemin may be necessary during acute episodes to suppress porphyrin synthesis, although its use should be carefully monitored due to possible side effects.

Genetic basis

This disease follows an autosomal dominant mode of inheritance. Autosomal dominant inheritance means that cats only have to inherit one copy of the mutation or pathogenic variant to be at risk of developing the disease. Each kitten born to a parent carrying one copy of the mutation has a 50% chance of inheriting one copy of the mutation and being at risk for the disease. Breeding between cats carrying genetic variants that can cause disease is not recommended, even if they do not show symptoms.

Technical report

Acute intermittent porphyria (AIP) is an inherited metabolic disorder characterized by a decrease in the activity of the enzyme hydroxymethylbilane synthase (HMB-synthase), which plays a crucial role in the heme group biosynthesis pathway. This disease belongs to the group of acute hepatic porphyrias and is characterized by the accumulation of porphyrins. Biochemical and genetic studies revealed a halved HMB-synthase activity in affected cats, with mutations identified in HMB-synthase genes in each porphyric line. Here, we studied the variant c.826-1G>A, which affects position 1 of the splice site of exon 14. This mutation results in a change in reading frame and a premature stop codon at codon 281.

Most affected breeds

Domestic Shorthair
Siamese

Bibliography

Clavero S, Ahuja Y, Bishop DF, et al. Diagnosis of feline acute intermittent porphyria presenting with erythrodontia requires molecular analyses. Vet J. 2013 Dec