FGFR3 and periodic paralysis: These include loss-of-function mutations of the porcine ryanodine receptor and equine skeletal muscle sodium channel alpha subunit gene causing, respectively, malignant hyperthermia and hyperkalaemic periodic paralysis in homozygotes, yet increased muscle mass in heterozygotes [12],[13], or of a FGFR3 mutation causing hereditary chondrodysplasia in homozygous sheep and increased size in the carriers [14],[15].