Test Detail

Hereditary myopathic hypokalemia, initially described in the Burmese, is a disease that alternates episodes of generalized muscle weakness with drops in blood potassium. It affects skeletal muscle: affected cats suffer crises of weakness with ventral flexion of the neck, hunched postures and inability to jump or walk normally. Episodes last from hours to days and are usually triggered by stress or exercise. With potassium supplementation and adequate management the prognosis is good, but the disease accompanies the animal for life.

Breed of origin: Burmese. The variant has also been detected in breeds on the test list: Australian Mist, Cornish Rex, Devon Rex, Singapura, Sphynx and Tonkinese, generally through common ancestry or introgression of Burmese lines. Carrier frequencies vary by country; published data outside the Burmese are limited.

- Episodes of generalized muscle weakness, lasting from hours to days
- Ventral flexion of the neck (the cat cannot hold its head upright)
- Hunched posture, refusal to jump, stiff gait
- Myalgia and sensitivity to muscle palpation
- Stress or exercise as common triggers
- First crisis usually in young cats

The disease was recognized in the 1990s in Burmese cats in Australia and New Zealand as a familial episodic myopathy, and its recessive hereditary nature was established through pedigree analysis. The response to potassium supplementation confirmed the hypokalemic mechanism of the crises. In the 2010s the responsible mutation was identified in the WNK4 gene, implicated in renal potassium handling, which enabled the DNA test. The test revealed the presence of the allele in breeds related to the Burmese and in populations where the breed had been used in crosses.

- Test breeding animals of the at-risk breeds: it distinguishes clear, carriers and affected.
- Never cross two carriers; a carrier with value can be crossed with a clear one without risk of affected cats.
- Test offspring that remain in breeding and record the result in the pedigree.
- Affected cats can have a good quality of life with potassium supplementation and veterinary monitoring, but must not be used in breeding.

Differential diagnosis with other feline myopathies (congenital myotonia, dystrophies), polyneuropathies, hypokalemias secondary to renal or digestive disease or diuretics, and with thiamine/nutritional deficiencies. During the crisis, low serum potassium (typically below the reference range) together with cervical flexion supports the diagnosis; creatine kinase may be elevated. Avoid prolonged fasting, stress and potassium-poor diets in affected cats.

1. Gandolfi B et al. (2012) First WNK4-hypokalemia animal model identified by genome-wide association in Burmese cats. PLoS One 7(12):e53173. PMID: 23285264
2. Malik R et al. (2015) Periodic hypokalaemic polymyopathy in Burmese and closely related cats: a review including the latest genetic data. J Feline Med Surg 17(5):417-426. PMID: 25896241
3. OMIA:001759-9685 — Hypokalaemic periodic paralysis in Felis catus.