Association of the DMRT3 nonsense mutation with pattern of locomotion in five different horse breeds

Abstract: A nonsense mutation in the DMRT3 gene has been shown to have a large impact on pattern of locomotion in horses. Horses that can perform several other gaits in addition to the normally occurring gaits, walk, trot and canter, are often hetero (CA)- or homozygous (AA) for this nonsense mutation. Horses that only can perform walk, trot and canter are often homozygous for the wild-type gene (CC). For example the Icelandic Horse is a gaited breed. Five-gaited Icelandic horses can perform both flying pace and tölt, except for the normally occurring gaits, walk, trot and canter, and are often homozygous for this nonsense mutation (AA). Four-gaited Icelandic horses can only perform tölt, in addition to walk, trot and canter and are often heterozygous (CA) for the mutation. Four-gaited Icelandic horses can also be homozygous for the wild-type gene (CC). In this study the significance of the DMRT3-mutation for how easy the Icelandic horse is to start tölt with has been tested. We also studied Standardbreds and Coldblooded trotters without the right genetic prerequisites to trot really fast on the racetracks to see if the mutation was significant for how easily they could be retrained to riding horses due to a better canter. The significance of the nonsense mutation has also been tested for the Morgan and American Curly to see if it has anything to do with how gaited the horses are. The study involved collection of hair samples and phenotypic description through questionnaires. In this study 263 hair samples have been analyzed. It has been shown that Icelandic horses homozygous for the wild-type gene are more difficult to put into tölt compared with horses that are hetero- or homozygous for the nonsense mutation. Standardbreds heterozygous for the DMRT3-mutation has been shown to be more easily retrained to riding horses due to a better canter compared to trotters that are homozygous for the nonsense mutation. The frequency of the DMRT3-mutation has been shown to have a large impact on how gaited the horse becomes in Morgans and American Curly.