Familial incidence of hyperkalemic periodic paralysis in quarter horses.

The pedigrees of 17 horses with hyperkalemic paralysis were studied. All were first-, second-, or third-generation offspring of a common sire, 16 were registered Quarter Horses. Analysis indicated that it was unlikely that the concentration of hyperkalemic periodic paralysis in the offspring of this sire was attributable to chance. The familial nature of this condition should help veterinarians diagnostically. It also suggests that it is possible to reduce the incidence of this condition by breeding from non-affected lines of horses and reinforces the need for studies to determine whether the disease is genetic in origin. Although more affected horses were second-generation offspring, the proportion of horses affected was largest in the first generation and decreased progressively with each generation. This is probably because horses in the earlier generations have been observed for longer periods and thus clinical signs are more likely to have been noticed in these horses.