Myostatin, or growth and differentiation factor 8 (GDF8), has been identified as the factor
causing a phenotype known as double muscling, in which a series of mutations render the
gene inactive, and therefore, unable to regulate muscle fibre deposition. This phenotype
occurs at a high frequency in some breeds of cattle such as Belgian Blue and Peidmontese.
Phylogenetic analysis has shown that there has been positive selection pressure for nonsynonymous
mutations within the myostatin gene family, around the time of the divergence
of cattle, sheep and goats, and these positive selective pressures on non-ancestral myostatin
are relatively recent. To date, there have been reports of nine mutations in coding regions of
myostatin that cause non-synonymous changes, of which three cause missense mutations,
including two in exon 1 and one in exon 2. The remaining six mutations, located in exons 2
and 3, result in premature stop codons, which are the mutations responsible for the doublemuscling
phenotype. Unfortunately, breed management problems exist for double-muscled
cattle, such as birthing difficulties, which can be overcome through genetically controlled
breeding programmes, as shown in this review.