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Phenotype: Occipitoatlantoaxial malformation (OAAM) is a developmental defect that results in the compression of the upper cervical cord and subsequent neurological damage including incoordination and weakness of the limbs. Affected individuals demonstrate abnormal head and neck carriage with neck extended, reluctance to move the neck, or signs of neck twisting.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal/Unaffected, OAAM = Occipitoatlantoaxial malformation
Breeds appropriate for testing: Arabian, Arabian crosses
Explanation of Results:
- Horses with N/N genoytpe will not have this form of occipitoatlantoaxial malformation and cannot transmit this occipitoatlantoaxial malformation variant to their offspring.
- Horses with N/OAAM genotype will not be affected by this form of occipitoatlantoaxial malformation, but are carriers. They may transmit this occipitoatlantoaxial malformation variant to 50% of their offspring. Matings between two carriers result in a 25% chance of producing a occipitoatlantoaxial malformation-affected foal.
- Horses with OAAM/OAAM genotype will have this form of occipitoatlantoaxial malformation.
$40 one test per animal
+ $20 each additional test from list below:
$80 entire Arabian Health Panel (all 4 tests)
Occipitoatlantoaxial malformation (OAAM) is a developmental defect in which the first cervical vertebra (atlas) resembles the base of the skull (occiput) and the second cervical vertebra (axis) resembles the atlas. This abnormal structure causes compression of the upper cervical cord, which leads to neurological damage. Affected individuals demonstrate abnormal head and neck carriage with neck extended, reluctance to move the neck, or signs of neck twisting. Movement of head and neck can also produce a clicking sound. Clinical signs vary from mild progressive incoordination and weakness of limbs to the inability to stand.
Additional information about OAAM is available at:
OAAM is presumed to be inherited as an autosomal recessive defect in Arabian horses, but different mutations appear to be involved. One such variant has been identified by researchers at the School of Veterinary Medicine, University of California, Davis. This variant, associated with one form of OAAM in Arabians, consists of a large deletion in the homeobox gene cluster (HOX). The genetic basis of other forms of OAAM are under investigation.
Testing for this identified OAAM variant can help breeders and owners detect carrier horses and select mating pairs accordingly to avoid producing OAAM-affected foals. Matings between two carriers of this particular mutation have a 25% percent chance of producing OAAM foals. The test is recommended for horses in Arabian lineages that have produced OAAM affected foals.
|Test Result||Occipitoatlantoaxial Malformation (OAAM)|
|N/N||Normal. Horse does not have the OAAM gene.|
|N/OAAM||Carrier. Horse carries 1 copy of the OAAM gene.|
|OAAM/OAAM||Affected. Horse has 2 copies of the OAAM gene.|
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