Occipitoatlantoaxial malformation


Good news!   

Your horse is clear of occipitoatlantoaxial malformation and does not have the mutated gene.

Your horse cannot pass on this mutation.

There are no breeding or performance implications

What is occipitoatlantoaxial malformation?

Occipitoatlantoaxial malformation (OAAM1) is an inherited genetic disease caused by the HOXD3 gene that causes the vertebrae in a horse’s Spinal column to fuse together, resulting in a loss of coordination and sometimes paralysis. Symptoms range from mild incoordination and weakness of the limbs, to paralysis of both front and hind legs. Mild cases may not show manifestations of the disease until the horse is several years old.

Genomic Details

The mutation thought to cause OAAM1 is a deletion in HOXD3 gene. This is when part of the gene is deleted. This deletion is associated with OAAM1. How the gene mutation causes OAAM1 is not known. In fact, some Arabian horses with this mutation can have a less severe form of OAAM1. Moreover, there are other types of occipitoatlantoaxial malformation that are not caused by this specific deletion.

A horse’s genetic result for OAAM1 is one of three possibilities:

  • Not deleted / Not deleted: Does not have the disease. Does not have the mutation.

  • Not deleted / Deleted: Carrier. Does not have the disease. Carries one gene mutation from one parent. This might be passed to the foal.

  • Deleted / Deleted: Affected. Has the genetic disease. The horse has inherited a gene mutation from each parent. One mutation will be passed to their foal.