The myostatin protein has been shown to affect both the amount and composition of muscle fibers.
Such variants have been observed in mice, cattle, sheep, and human, the latter described once in a German boy. The “bully” whippet phenotype is reminiscent of the double muscling phenotype seen in other species that is caused by mutations in the myostatin (MSTN) gene. (C) Dogs are homozygous for the mutant allele with two copies of the cys → stop mutation (mh/mh).Īll photos represent unique individuals except for the top and middle panels in the righthand column. (B) Dogs are heterozygous with one wild-type allele and one mutant cys → stop allele ( mh/+). (A) Dogs have two copies of the wild-type allele (+/+). In addition, about 50% of “bully” whippets have a distinctive overbite.Ĭomparison of Whippets with Each of the Three Potential Genotypes However, the dogs are often euthanized at an early age as they do not conform to the American Kennel Club breed standard. Owners report that “bully” whippets do not have any health abnormalities other than muscle cramping in the shoulder and thigh. “Bully” whippets are easily distinguished from their normal littermates based on physical appearance alone (compare Figure 1A and and1C). Heavily muscled dogs, termed “bully” whippets by breeders, have broad chests and unusually well-developed leg and neck musculature ( Figure 1C). The typical whippet is similar in conformation to the greyhound, a medium-sized sighthound, weighing about 9 kg and characterized by a slim build, long neck, small head, and pointed snout ( Figure 1A). Recently, owners of whippets, an established racing-dog breed, have reported a phenotype of heavy muscling occurring within the breed ( ). The wide variety of behaviors and morphological types exhibited among dog breeds and the overall low genetic diversity within each breed make the dog an excellent genetic system for mapping traits of interest.
However, as little is known about the health issues and potential risks associated with being a myostatin-mutation carrier, research in this arena should proceed with extreme caution. Future implications include screening for myostatin mutations among elite athletes. Further, it emphasizes what is sure to be a growing area of research for performance-enhancing polymorphisms in competitive athletics. This result is the first to quantitatively link a mutation in the myostatin gene to athletic performance.
However, dogs with two copies of the same mutation are grossly overmuscled, superficially resembling double-muscled cattle known to possess similar mutations. Dogs that possess a single copy of this mutation are more muscled than normal and are among the fastest dogs in competitive racing events. We have discovered a mutation in the canine myostatin gene, a negative regulator of muscle mass, which affects muscle composition, and hence racing speed, in whippets. The purebred dog has a long history of selective breeding, which has produced specific breeds of extraordinary strength, intelligence, and speed. The canine species presents an excellent system in which to find such associative genes. An individual's genetic profile can play a role in defining their natural skills and talents.