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Hydrocephalus (HCP Horse)

In hydrocephalus, cerebrospinal fluid accumulation in the brain leads to enlarged skull and death of the foal. The disease occurs in Friesian horses and is inherited autosomal recessively.


Genetic Test: Currently not available (Contact us for more information.)


  • Enlarged skull
  • No chance of survival

General Information

  • 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.

Breeds affected

Friesian Horse

Test Information

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

Genotype and Lab Report

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.




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.

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