Hydrocephalus (HCP Horse)

• Enlarged skull
• No chance of survival

• Hydrocephalus is composed of the Greek hydōr (= water) and kephalē (= head) and thus means as much as "water head".
• Fluid exerts pressure on brain and skull.
• Affected foals are stillborn.
• The large head can lead to problems during birth → endangers mare.

This test detects the change of a single basepair (c.1423C>T) in exon 12 of the B3GALNT2 gene.

Inheritance: autosomal recessive

→ Only animals with two copies of the variant (hcp/hcp) are affected. Animals with only one copy of the variant (N/hcp) are clinically normal carriers.

Genotype

N/N = normal

The horse has no copies of the genetic variant causitive for HCP and therefore cannot pass it on to its offspring.

N/hcp = a carrier

The horse is clinically healthy.  It has one copy of the genetic variant causitive for HCP, which will be passed on to its offspring with a probability of 50%.

hcp/hcp = affected

The horse is affected and has two copies of the genetic variant causitive for HCP.  The variant will be passed on to its offspring with a probability of 100%. All offspring will be carriers.

• Carriers may be bred to normal animals (N/hcp x N/N) without any risk of producing affected offspring. The offspring should also be tested before breeding to determine if they are carriers or normal.
• Breeding two carriers (N/hcp x N/hcp) is not recommended due to the possibility of 25% of the offspring being affected.

Ducro, B.J., Schurink, A., Bastiaansen, J.W., Boegheim, I.J., van Steenbeek, F.G., Vos-Loohuis, M., Nijman, I.J., Monroe, G.R., Hellinga, I., Dibbits, B.W., Back, W., Leegwater, P.A.: A nonsense mutation in B3GALNT2 is concordant with hydrocephalus in Friesian horses. BMC Genomics 16:761, 2015. Pubmed reference: 26452345. DOI: 10.1186/s12864-015-1936-z.

Further information is available at Online Mendelian Inheritance in Animals.