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
More Horse Health
Congenital Stationary Night Blindness 2
Congenital Stationary Night Blindness (CSNB) is an inherited disorder in horses characterized by an inability to see in low-light or dark conditions. This condition is present from birth and does not worsen over time. Common indicators include a horse’s reluctance to enter dark environments, difficulties in locating food and water in the dark, and a propensity for nighttime injuries.
Equine Arteritis Virus Resistance
Equine Arteritis Virus Resistance (EAVR) is an infectious disease with a broad range of symptoms, though most horses will not display any overt signs. Infection can result in abortion in pregnant mares, and some stallions persistently shed the virus through their semen.
Equine Herpes Virus Type 1 & Induced Myeloencephalopathy
Equine herpesviruses are DNA viruses that are found in most horses all over the world, often without any serious side effects. Following infection of Equine Herpesvirus Type 1 (EHV-1) some horses then suffer Equine Herpesvirus Myeloencephalopathy (EHM), which is is accompanied by serious and sometimes fatal neurological effects. EHM in horses can have serious neurological symptoms on affected horses.