Hydrocephalus (HCP)

Description

Hydrocephalus is a developmental disorder involving an accumulation of cerebrospinal fluid within the skull. Affected horses have a narrowing of the pathway through which cerebrospinal fluid normally travels, causing fluid to accumulate and distend the skull. This often results in foals born prematurely, stillbirth of affected foals, and dystocia in dams during the birthing process.

The condition is caused by a nonsense variant in the β-1,3-N-acetylgalactosaminyltransferase 2 gene, B3GALNT2 c.1423C>T (p.Gln475*), which introduces a premature stop in the protein. The same variant has been identified in a human case of muscular dystrophy-dystroglycanopathy with hydrocephalus. Its prevalence in Friesians is primarily a result of a founder effect and years of inbreeding, with the widespread use of only a few influential ancestors. The estimated carrier frequency in the Friesian population is around 17%.

Hydrocephalus is inherited as an autosomal recessive trait, so a foal must inherit two copies of the variant to be affected. Carriers have one copy and show no signs of the disorder. If two carriers are bred, each foal has a 25% chance of being affected and a 50% chance of being a carrier. Because affected foals do not survive, DNA testing of breeding stock is the only way to identify carriers and avoid pairing them.

There are several different forms of hydrocephalus in horses. This test identifies only the B3GALNT2 variant documented in Friesian horses and will not detect carriers of other forms. Testing is valid for Friesian horses and horses with Friesian ancestry.

Possible results

Breeds Affected

Appaloosa/Friesian, Arabian/Friesian Cross, Baroque Pinto, Belgian Draft Horse, Friesian, Friesian Cross, Moriesian, Stonewall Sporthorse, Warlander

Reference

A nonsense mutation in B3GALNT2 is concordant with hydrocephalus in Friesian horses.

[PMID: 26452345]