A mutation in the myostatin gene increases muscle mass and enhances racing performance in heterozygote dogs

Double muscling is a trait previously described in several mammalian species including cattle and sheep and is caused by mutations in the myostatin ( MSTN) gene ( previously referred to as GDF8). Here we describe a new mutation in MSTN found in the whippet dog breed that results in a double- muscled phenotype known as the bully'' whippet. Individuals with this phenotype carry two copies of a two- base- pair deletion in the third exon of MSTN leading to a premature stop codon at amino acid 313. Individuals carrying only one copy of the mutation are, on average, more muscular than wildtype individuals ( p = 7.43 x 10(-6); Kruskal- Wallis Test) and are significantly faster than individuals carrying the wild type genotype in competitive racing events ( Kendall's nonparametric measure, tau = 0.3619; p approximate to 0.00028). These results highlight the utility of performance- enhancing polymorphisms, marking the first time a mutation in MSTN has been quantitatively linked to increased athletic performance.