Occipitoatlantoaxial Malformation 1 (OAAM1)
Gene or Region: HOX
Reference Variant: REF
Mutant Variant: ALT
Affected Breeds: Arabians, Arabian Crosses, Trakheners, breeds with Arabian heritage
Research Confidence: High - Findings reproduced in multiple studies
Explanation of Results: oaam1/oaam1 = homozygous for Occipitoatlantoaxial Malformation 1, trait expressed oaam1/n = heterozygous for Occipitoatlantoaxial Malformation 1, carrier n/n = no variant detected
General Description for Occipitoatlantoaxial Malformation 1
Occipitoatlantoaxial Malformation 1 (OAAM1) is an inherited developmental condition predominantly found in Arabian horses, characterized by abnormal development of the cervical vertebrae leading to compression of the upper cervical cord and subsequent neurological damage. This condition results in distinct symptoms such as an abnormal extension of the neck, reluctance or difficulty in neck movement, and potential twisting of the neck. Affected horses may also exhibit neurological signs including incoordination and weakness in the limbs.
OAAM1 is believed to be inherited in an autosomal recessive manner within the Arabian breed, though multiple mutations may be involved. Research has identified a significant deletion within the homeobox gene cluster (HOX) as one variant associated with this condition in Arabian horses. This discovery allows for genetic testing to identify carriers of the OAAM variant, enabling breeders to make informed decisions to prevent producing affected offspring. Breeding two carriers of this mutation carries a 25% risk of resulting in foals affected by OAAM1. Testing is especially advised for Arabian horses with a known lineage of OAAM1-affected individuals.
References
Bordbari, M. H., Penedo, M.C.T., Aleman, M., Valberg, S. J., Mickelson, J., & Finno, C. J. (2017). Deletion of 2.7kb near HOXD3 in an Arabian horse with occipitoatlantoaxial malformation. Animal Genetics, 48: 287–294. doi: 10.1111/age.12531
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