Breeds Affected: Whippet
Samples Accepted: Blood, Buccal Swabs
Disease Information: Muscular hypertrophy causes an enlargement of muscle cells, resulting in the phenotype of double muscling. Heterozygote animals are muscled more heavily than normal, which can give an advantage in racing, but animals with two copies have such enlarged muscles they are referred to as “bully” whippets. These animals are not able to race well due to muscle spasms, and approximately half also have an overbite.
Inheritance Information: Muscular Hypertrophy is incomplete autosomal dominant. This means that animals with one copy of the gene show a mild variation of the condition, and animals with two copies of this allele will be affected.
The possible genotypes are:
N/N The dog is normal, and cannot produce affected offspring.
N/mh The dog is mildly affected, and can pass the allele on to approximately 50% of any offspring. If bred to another N/mh dog, approximately 25% of the offspring will be normal, 50% will be mildly affected, and 25% will be affected.
mh/mh The dog is affected, and if bred to a normal animal, 100% of the offspring will be mildly affected. If bred to an N/mh dog, 50% of the offspring will be mildly affected and 50% will be affected.
– Mildly affected animals may be bred to normal animals (N/mh x N/N) without the risk of producing affected offspring.
– Breeding two mildly affected dogs (N/mh x N/mh) is not recommended due to the possibility of 25% of the offspring being affected.
– Affected animals (af/af) should not be used for breeding.
Test Information: This test identifies a 2 base deletion in the MSTN gene.
Mosher, DS., Quignon, P., Bustamante, CD., Sutter, NB., Mellersh, CS., Parker, HG., Ostrander, EA.: A mutation in the myostatin gene increases muscle mass and enhances racing performance in heterozygote dogs. PLoS Genet 3:e79, 2007. Pubmed reference: 17530926. DOI: 10.1371/journal.pgen.0030079
Shelton, GD., Engvall, E.: Gross muscle hypertrophy in whippet dogs is caused by a mutation in the myostatin gene. Neuromuscul Disord 17:721-2, 2007. Pubmed reference: 17651971. DOI: 10.1016/j.nmd.2007.06.008
Further information is available at the Online Mendelian Inheritance in Animals website.