Credit: BLICKWINKEL/ALAMY

Whippets are fast — these dogs can run at speeds of more than 60 kilometres per hour, and have long been used in racing. But, recently, owners have been reporting an increase in 'double muscling', a trait characterized by cramping in the shoulders and thighs of otherwise healthy whippets. Dana Mosher and colleagues now show that a mutation in the MSTN gene is the culprit (D. S. Mosher et al. PLoS Genet. e79.eor doi:10.1371/journal.pgen.0030079.eor; 2007).

The MSTN gene encodes myostatin, a protein that affects muscle composition. Mosher et al. analysed the sequence of MSTN from three categories of whippet: the heavy-muscled 'bully' whippets, which have double muscling; parents of bully whippets; and normal whippets unrelated to bullies.

They found that all bully whippets carry a mutation in both copies of the MSTN gene, and all bully-whippet parents have the same mutation in one copy of this gene. This mutation involves deletion of only two DNA base pairs, resulting in premature termination of messenger RNA translation and a truncated form of myostatin.

Looking for a correlation between this MSTN mutation and whippets' racing performance, the authors observed a significant association between the dogs' speed, their muscle mass and their genetic profile. Whippets with one mutated copy of MSTN were generally the fastest, followed by normal animals. Bully whippets are rarely raced, probably because they are handicapped by an excess of muscle. The increase in the incidence of the MSTN mutation is probably due to selective breeding of whippets.

Mosher et al. did not detect this mutation in 14 other heavy-muscled breeds of dog, suggesting that it might be unique to whippets. There is the question of whether a similar mutation in humans could be exploited to enhance athletic performance. However, the authors caution that effects of the MSTN mutation on other aspects of health are unknown.