Good news!   

Your horse is clear of hydrocephalus and does not have this gene mutation.

Your horse cannot pass on this mutation. There are no breeding or performance implications.

What is hydrocephalus?

Hydrocephalus affected foals are easily identifiable by their large foreheads, caused by the buildup of fluid in the skull. This distension of the skull can lead to fatal complications for the mother during birth. Affected foals are often stillborn or are humanely euthanized at birth to save the mare. Foals that survive birth frequently have severe neurological defects.  

Genomic Details

Hydrocephalus is caused by a mutation in the B3GALNT2 gene that is on chromosome 1. Horses with this mutation have an abnormal amount of cerebrospinal fluid in their head. This can be due to overproduction or inadequate absorption of cerebrospinal fluid. Sometimes, the passage where the head meets the neck is too narrow. This buildup of fluid causes a large, swollen head.

The mutation that causes hydrocephalus is a switch in one of the four base pairs that make up a DNA molecule. Cytosine (C) is replaced by Thymine (T) changing the B3GALNT2 gene. Therefore, a horse’s genetic result for hydrocephalus is one of three possibilities:

  • C/C: Normal. Does not have the disease. Does not have the mutation.

  • C/T: Carrier. Does not have the disease. Carries one gene mutation from one parent. This might be passed to their foal.

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