Acute Intermittent Porphyria (Variant 4)

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 dominant 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.

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 dominant meaning that one copy of the mutation is needed for disease signs to occur. Use of cats with one or two copies of the disease mutation is not recommended, as there is a risk that the resulting litter will contain affected kittens. For example if a cat with one copy of the AIP mutation is bred with a clear cat with no copies of the AIP mutation, about half of the kittens will have one copy and half will have no copies of the AIP mutation. 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.