Hydrocephalus in Friesian Horses
Summary
Hydrocephalus in Friesian horses is an inherited developmental disorder that often results in stillbirths of affected foals and obstructed labor (dystocia) in dams, which can be fatal to the dam during birth. Hydrocephalus is a distension of the ventricular system of the brain with cerebrospinal fluid. The increased intracranial pressure inside the skull leads to enlargement of the head. The condition is usually fatal. There is no effective treatment.
About 15% of Friesian horses are carriers of the recessive trait. Hydrocephalus has been seen rarely in other breeds, although it is unclear whether it has the same genetic basis.
Date of Last Update: 08/02/2016
Results
Understanding the Results
Results of the genetic test for Hydrocephalus in Friesian horses are presented as shown below.
| Hydrocephalus in Friesian horses | ||
|---|---|---|
| N/N | Clear | This horse tested negative for Hydrocephalus. |
| N/HCP | Carrier | Both the normal and mutant alleles are present. This horse is positive for the Hydrocephalus mutation but will not develop symptoms. |
| HCP/HCP | Affected | This horse carries two copies of the Hydrocephalus mutation and will die of the disease. |
Disease Name and Genes
Hydrocephalus in Friesian horses is associated with a C to T substitution that changes a Glutamine (Q) codon to a termination codon at amino acid position 475 of the B3GALNT2 gene (B3GALNT2-Q475X).
Inheritance
Hydrocephalus in Friesian horses is caused by a recessive variant of the B3GALNT2 gene (B3GALNT2-Q475X). The recessive allele is commonly abbreviated as HCP, with the dominant wild-type allele abbreviated as N.
Carriers of the recessive allele (N/HCP) have no symptoms of the disease. If two carriers are bred, each foal has a 25% chance of having two copies of the normal allele (N/N), a 50% chance of being a carrier (N/HCP), and a 25% chance of being affected (HCP/HCP).
If a carrier of the recessive allele (N/HCP) is bred to a normal horse (N/N), each foal has a 50% chance of having two copies of the normal allele (N/N) and a 50% chance of being a carrier (N/HCP).
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