Hydrocephalus / water on the brain (B3GALNT2-related) - Friesian horse

What does this test analyse?

This genetic test analyses the B3GALNT2 variant c.1423C>T for hereditary hydrocephalus, also known as water on the brain or congenital hydrocephalus, in Friesian horses.

Hydrocephalus means abnormal accumulation of cerebrospinal fluid in and around the brain. In affected foals this can lead to a severely enlarged, dome-shaped skull, stillbirth, non-viable foals and difficult birth for the mare.

Why is this test useful?

The disorder is autosomal recessive. Carriers are healthy in appearance, but two carriers can produce an affected foal. The test is therefore especially valuable before planning a mating: it shows whether a mare or stallion can be used safely with a specific partner.

Practical value of this test

• Breeders can avoid carrier x carrier matings and strongly reduce the risk of affected foals.
• The test supports stallion choice and mare selection within the Friesian population.
• A carrier can be used responsibly with a clear partner, so valuable lines do not need to be lost unnecessarily.
• The result supports clear communication for sale, breeding advice and studbook planning.
• In lines with stillbirth, hydrocephalus or difficult foaling, the test can make hereditary risk concrete.

Inheritance and result

The result is reported as N/N, N/HCP or HCP/HCP. N/N means that the variant was not detected. N/HCP means carrier: the horse is not affected but can pass the variant on. HCP/HCP causes hereditary hydrocephalus and is a severe outcome in foals.