NEUROMUSCULAR CASE OF THE MONTH – MAY 2007

Mutations in the gene for myostatin cause gross muscle hypertrophy in Whippets
Contributed by Dr. Eva Engvall
Burnham Institute for Medical Research, La Jolla, CA

The Whippet is a smaller, Greyhound-like dog, famous for its speed of running and ability of catching small game. Heavily muscled dogs have appeared in certain lines of the Whippet breed from time to time. Many have thought that the heavy muscling of these Whippets is a throwback to the times when Whippets were mated with muscular dogs of other breeds to obtain the strength necessary for running. However, it has now been shown that the double-muscled (DM) Whippets are homozygous for a mutation in the gene for myostatin. This mutation is relatively recent and is unique to the Whippet breed, and not found in any of several other breeds of dogs, including dogs with heavy muscle mass.

Double-muscled Whippet

Whippet with normal muscle mass

Many factors control muscle development and regeneration.  Myostatin is one, and it is a negative regulator of muscle mass. When myostatin is mutated or absent, the muscle grows to excessive size. Myostatin has long been of interest in the cattle industry, as myostatin deficient “double muscled” cattle, such as the Belgian Blue, produce extraordinary amounts of high quality meat.  There are some health concerns for the double muscled cattle, including problems with calving. The DM Whippets may suffer from occasional cramping and stiffness, but appear otherwise healthy and have a normal life span. They are obviously not used for breeding, as they are not very attractive looking. Interestingly, the DM Whippets have exceptionally sweet temperament, and they are in this regard very different from dogs of other breeds that have been selected for muscle mass and strength.  The mutation in the DM Whippets seems to have been carried along for generations, particularly in racing lines, as the heterozygous mutant Whippets seem to have an advantage in racing. In contrast, Whippets with the mutation have no advantage in conformation, and the mutation is not present in lines of show Whippets. 

For references to the literature, see Shelton GD and Engvall E, Neuromuscular Disorders (2007) 17:721-722. The image of the double-muscled Whippet is courtesy of the Veterinary Information Network and the normal Whippet courtesy of Lee Anne Norris.  

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