Hypokalaemia or  hypokalemic polymyopathy (BHP)

Hypokalaemia refers to the condition in which the concentration of potassium ions in the blood serum is low and most often occurs as a secondary problem, but it can occur as a primary hereditary familial disease, e.g. hypokalemic periodic paralysis (HPP) in humans or hypokalemic periodic polymyopathy in cats BHP - Burmese Hypokalaemic Polyomyopathy).

The most characteristic clinical sign of BHP disease is a skeletal muscle weakness that is frequently episodic in nature, either generalized, or sometimes localized to the neck and thoracic muscles.

In connection with the BHP disease, a mutation (c.2899C>T) in WNK4 gene was found producing a premature stop codon, leading to a protein from the family of serine/threonine kinase truncated by an important domain and a phosphorylation site (Gandolfi et al. 2012).

The feline model of hypokalaemia is the first animal model of this disease and it is assumed that the revealed mutation may help to clarify to role of the protein in K⁺ regulation and the mechanism causing the disease (Gandolfi et al. 2012).

The breeds that are at risk for BHP include: Burmese and outcrosses such as Burmilla, Bombay, Cornish Rex, Devon rex, Singapura, Sphynx, Australian Mist, Tiffanie and Tonkinese.

The clinical signs of BHP are in most cases episodic, but in some cats the muscle weakness may persist. During an episode, muscle pain (myalgia) from palpation can be a prominent sign. Cats can present with severe generalized muscle weakness, often restricted to the neck and chest area that is evidenced by ventroflexion of the head and neck (the cat is unable to hold its head up), head bobbing and protrusion of the bladebone (a bladebone sticking out of the animal's back). The gait becomes stiff and accompanied with a muscle tremor. The cats have crouching gait, especially evident in the hind limbs. During an episode, the onset and the severity of the clinical signs are influenced by the rate with which the K+ concentration in the blood serum decreases. The serum potassium usually spontaneously normalizes after an episode. The clinical signs of BHP become usually evident when kittens are two to six months of age, although some cases have not been detected until 2 years of age. The clinical signs may be triggered by stress or exercise.

The disease is not fatal and the potassium can usually be managed by adding potassium supplements to the diet, but always consult your vet, who examines the health condition of the affected cat.

BHP is an autosomal recessive disorder. The disease affects cats with P/P (positive / positive) genotype only. Cats with P/N (positive /negative) genotype are clinically without any symptoms. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

.

Reference:

Gandolfi B, Gruffydd-Jones TJ, Malik R, Cortes A, Jones BR, et al. (2012) First WNK4-Hypokalemia Animal Model Identified by Genome-Wide Association in Burmese Cats. PLoS ONE 7(12): e53173. doi:10.1371/journal.pone.0053173