Gene or region: DMRT3
Reference allele: C
Mutant allele: A
Affected Breeds: Many
Research Confidence: High confidence, findings reproduced in multiple studies
What it does:
Horses display a wide variation in locomotion, with “gaited” breeds displaying a range of unique footfall patterns at intermediate speeds. Even amongst the non-gaited (trotting) breeds, some individuals are capable of lateral movements. Also, while most horses will shift into the three beat canter at higher speeds, some horses are able to remain in their intermediate gaits (for example, harness racing breeds) without breaking into a canter.
DMRT3 is a transcription factor located within the spinal cord. Mice lacking Dmrt3 display incoordination of the limbs and difficulty running at higher speeds. In the Icelandic Horse, the C allele is associated with better synchronization of diagonal legs and higher ratings of the trot and gallop, whereas the A allele is associated with higher speed and coordination at the tölt (a lateral intermediate gait). This mutation results in a premature stop codon, which truncates the encoded protein.
The exact phenotype of the DMRT3 mutation is somewhat controversial. Currently published research has identified this mutation as the casual variation responsible for the ability to perform intermediate lateral gaits. However, even within these studies, there were horses from gaited breeds that tested C/C at DMRT3, which should result in a horse that cannot perform a gait other than the trot. Also, this variation was originally identified in the Icelandic Horse as associated with the ability to perform a flying pace, which is a lateral intermediate speed gait performed at a higher speed. All Icelandic Horses in this study, even those unable to perform the flying pace, were able to perform the lateral tölt.
Additionally, preliminary testing has uncovered the DMRT3 mutation in breeds not known for gaiting. It is also suspected that there may be additional or different "gait" variations/genes still undiscovered in many breeds.
Andersson LS et al., “Mutations in DMRT3 affect locomotion in horses and spinal circuit function in mice.” (2012) Nature. 488: 642-6. PMID: 22932389
Promerová M et al., “Worldwide frequency distribution of the 'Gait keeper' mutation in the DMRT3 gene.” (2014) Anim Genet. 45: 274-82. PMID: 24444049
Kristjansson T et al., “The effect of the 'Gait keeper' mutation in the DMRT3 gene on gaiting ability in Icelandic horses.” (2014) J Anim Breed Genet. doi: 10.1111/jbg.12112. [Epub ahead of print] PMID: 25073639