Double muscling refers to an excessive buildup of skeletal muscle caused by a mutation of the myostatin gene. This mutation is most commonly found in cows and sheep, although it sometimes occurs in other mammalian species, including humans. In dogs, double muscling is primarily known to occur in the whippet, an athletic racing breed closely related to the greyhound.
Myostatin is a growth factor produced by skeletal muscle. Its normal function is to regulate muscle growth and prohibit excessive growth. Inhibition of this factor causes the skeletal muscle mass to increase and prevents the muscles from degenerating, which can lead to double muscling. This inhibition is caused by a mutation in the gene responsible for myostatin production, the MSTN gene, according to “PLOS Genetics.”
The whippet is a miniaturized version of the English greyhound. A whippet’s normal appearance is that of a sleek, medium-sized racing hound, with features similar in appearance to an English or Italian greyhound. This breed is susceptible to a mutation in the MSTN gene that causes excessive muscle buildup. Whippets with this mutation are commonly referred to as “bully whippets.”
Dogs having only one copy of this genetic mutation are incredibly athletic and ranked among the fastest racing dogs. Some whippets are born with two copies of the mutation, which causes them to be grossly overmuscled, according to “PLOS Genetics.” For those with a single copy of the mutation, the enhancements to athletic ability are so great that it has prompted further research into the role of performance-enhancing polymorphisms. In the future, this research may lead to screening elite athletes for the presence of myostatin mutations.
The study published in “PLOS Genetics” also revealed the existence of unrelated bully whippets in several breeding lines throughout North America and Europe, and their numbers appear to be growing. The cause of the mutation is currently unknown, and little is known about the long-term health implications to dogs that carry this mutation. This lack of information has prompted the formation of the Whippet Myostatin Project, an international group of whippet breeders and owners whose primary goal is development of a test to be able to identify carriers of this mutation. The organization is developing a database to collect and share information on mutated whippets worldwide, particularly how the dogs are affected by the mutation.
- PLOSGenetics.org: A Mutation in the Myostatin Gene Increases Muscle Mass and Enhances Racing Performance in Heterozygote Dogs
- PubMed: Myostatin inhibition by a follistatin-derived peptide ameliorates the pathophysiology of muscular dystrophy model mice.
- AKC.org: Get to Know the Whippet
- WhippetRacing.org: Whippet Myostatin Project (PDF)
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