Hereditary muscle disorder of the Burmese cat (and related breeds) caused by a loss of function of the WNK4 gene. It produces recurrent episodes of muscle weakness and paralysis due to hypokalemia (low blood potassium), with recovery between episodes. It is not a hypercalcemic periodic paralysis and does not involve calcium abnormalities. The test detects the causative allele and identifies carriers; it is complementary to, not a substitute for, clinical examination and blood work.

Applicable breed: Burmese and related breeds. Periodic hypokalemia is a recognised disease of the breed, but no carrier frequencies have been published systematically (limited data).

- Recurrent episodes of generalised muscle weakness (especially neck and limbs)\n- Stiff gait, inability to stand and, in severe crises, paralysis\n- Ventral flexion of the neck and difficulty raising the head\n- Marked hypokalemia during episodes (low serum potassium)\n- Normal or mildly elevated creatine kinase\n- Mental state and digestion preserved; recovery between episodes\n- Episodes may be triggered by stress, fasting or exertion

Feline periodic hypokalemia was recognised in Burmese cats with episodes of weakness and low potassium levels. In 2012, Gandolfi and colleagues identified through a genome-wide association study a nonsense variant in WNK4 as the cause of the condition, establishing the first natural animal model of WNK4-related hypokalemia. In 2015, Malik and colleagues reviewed the clinical presentation and genetic data in Burmese and related breeds. The carrier test is used in breeding of the breed.

- Test Burmese and related-breed breeding animals before mating\n- Do not cross two carriers: 25% affected homozygotes\n- A carrier may be crossed with a clear cat; test offspring intended for breeding\n- Exclude affected cats and known carriers from breeding\n- In carrier animals, avoid triggering factors (stress, prolonged fasting) and monitor serum potassium

Differential diagnosis with other causes of episodic weakness and hypokalemia in the cat (cauda equina lesions, digestive or renal potassium losses, myasthenia, toxins). Hypokalemia during the episode together with the Burmese breed point towards it; confirmation is molecular. Treatment of crises includes potassium supplements and management of the trigger. Do not confuse with hypercalcemic forms, which do not exist in the cat.

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):417-26. PMID: 25896241. OMIA:001759-9685.