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Acute Intermittent Porphyria (Variant 5)

Acute Intermittent Porphyria (AIP) is caused by faulty enzyme activity and results in brownish discoloration of the teeth and urine in affected cats.

Key Signs

Brownish teeth, Brownish urine, Anemia, Renal disease

Age of Onset

0 to 2 yrs

Juvenile onset

Inheritance

Autosomal Recessive

For autosomal recessive disorders, cats with two copies of the variant are at risk of developing the condition. Cats with one copy of the variant are considered carriers and are usually not at risk of developing the disorder. However, carriers of some complex variants grouped in this category may be associated with a low risk of developing the disorder. Individuals with one or two copies may pass the disorder-associated variant to their kittens if bred.

Likelihood of the Condition

Moderate likelihood

At risk cats may show signs of this disease in their lifetime, although some will not develop the condition due to absence of additional risk factors.

What to Do

Here’s how to care for a cat with AIP

Partner with your veterinarian to make a plan regarding your cat’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.

For Veterinarians

Here’s what a vet needs to know about AIP

Acute Intermittent Porphyria (AIP) is a hereditary disorder caused by the decreased activity of the hydroxymethylbilane synthase enzyme needed in the formation and excretion of porphyrins. Porphyrins, in combination with iron, form heme which then combines with other substances to make material that is essential for the normal function of cells. This decreased enzymatic activity leads to accumulation of its substrates in various tissues. Clinical signs are characterized by the brownish discoloration of the teeth and brownish urine. While these discolorations may be the only clinical signs for some, other affected cats develop more severe symptoms, including lethargy, anorexia, anemia, decreased hemoglobin, decreased iron, renal disease, and enlargement of the spleen and liver. Fluorescence of the bones and teeth is a specific diagnostic feature seen in affected cats. Various causative mutations for the disease have been found in cats, with this particular form of porphyria inherited in an autosomal recessive manner.

As there is no cure for this disease, therapy is limited to supportive care dictated by the severity of the clinical signs. Although described in other species, a propensity towards photosensitivity remains questionable in cats with this disorder. Owners may consider limiting exposure to sunlight in affected individuals.

For Breeders

Planning to breed a cat with this genetic variant?

There are many responsibilities to consider when breeding cats. Regardless of test results it is important that your cat is in good general health and that you are in a position to care for the kittens if new responsible owners are not found. For first time or novice breeders, advice can be found at most cat registry websites.

This disease is autosomal recessive meaning that two copies of the mutation are needed for disease signs to be shown. A carrier cat with one copy of the AIP mutation can be safely bred with a clear cat with no copies of the AIP mutation. About half of the kittens will have one copy (carriers) and half will have no copies of the AIP mutation. Kittens in a litter which is expected to contain carriers should be tested prior to breeding. Carrier to carrier matings are not advised as the resulting litter may contain affected kittens. Please note: It is possible that disease signs similar to the ones caused by the AIP mutation could develop due to a different genetic or clinical cause.

Technical Details

Gene HMBS
Variant G>A
Chromosome D1
Coordinate 16,541,613

All coordinates reference FelCat9.0

References & Credit

Credit to our scientific colleagues:

Clavero, S., Bishop, D. F., Haskins, M. E., Giger, U., Kauppinen, R., & Desnick, R. J. (2009). Feline acute intermittent porphyria: A phenocopy masquerading as an erythropoietic porphyria due to dominant and recessive hydroxymethylbilane synthase mutations. Human Molecular Genetics, 19(4), 584–596. View the article