Periodic paralysis in Quarter Horses: A sodium channel mutation disseminated by selective breeding

We recently reported on a linkage study within a Quarter Horse lineage segregating hyperkalaemic periodic paralysis (HYPP), an autosomal dominant condition showing potassium–induced attacks of skeletal muscle paralysis. HYPP co–segregated with the equine adult skeletal muscle sodium channel α subunit gene, the same gene that causes human HYPP. We now describe the Phe to Leu mutation in transmembrane domain IVS₃ which courses the horse disease. This represents the first application of molecular genetics to an important horse disease, and the data will provide an opportunity for control or eradication of this condition.