Hydrocephalus is an inherited condition in Friesian and Friesian crosses characterized by excessive accumulation of fluid in the brain that results in severe cranial distension.
Phenotype: Hydrocephalus is characterized by excessive accumulation of fluid in the brain that results in severe cranial distension. This condition often causes foals to be stillborn.
Mode of Inheritance: Autosomal recessive
Alleles:N = Normal/Unaffected, H = Hydrocephalus
Breeds appropriate for testing: Friesians, Friesian crosses
Explanation of Results:
Horses with N/N genotype will not have hydrocephalus and cannot transmit this hydrocephalus variant to their offspring.
Horses with H/N genotype will not exhibit the hydrocephalus phenotype, but are carriers. They may transmit this hydrocephalus variant to 50% of their offspring. Matings between two carriers result in a 25% chance of producing a hydrocephalus-affected foal.
Horses with H/H genotype will have hydrocephalus, foals are typically stillborn or euthanized at birth due to complications.
Hydrocephalus is a condition characterized by excessive accumulation of fluid in the brain that results in severe cranial distension. It is thought to occur because of an abnormal narrowing of the jugular foramen (opening at the base of the skull) and can lead to dystocia in dams pregnant with affected foals. This condition often causes foals to be stillborn or to be euthanized at birth due to problems during parturition. A mutation (c.1423C>T) in exon 12 of the β-1,3-N-acetylgalactosaminyltransferase 2 (B3GALT2) gene has been identified that is associated with this disorder. The mutation does not allow for the full-length protein to be produced, which compromises its normal function. Mutations in this gene also cause muscular dystrophy-dystroglycanopathy with brain abnormalities in humans.
Friesian hydrocephalus is inherited as an autosomal recessive trait. This means that affected foals have two copies of the defective gene and that the disorder occurs in males and females. It is estimated that about 17% of Friesian horses are carriers (N/H).
Testing for hydrocephalus is important to assist veterinarians in correct diagnosis and to assist owners in management and breeding decisions. Matings between two hydrocephalus carriers have a 25% chance of producing hydrocephalus-affected foals.
No copies of the hydrocephalus mutation. Horse is normal.
1 copy of the hydrocephalus mutation. Horse is normal but is a carrier.
2 copies of the hydrocephalus mutation. Horse is affected.
Boerma, S., Back, W., & Oldruitenborgh-Oosterbaan, M. M. (2011). The Friesian horse breed: A clinical challenge to the equine veterinarian? Equine Veterinary Education, 24(2), 66-71. doi: 10.1111/j.2042-3292.2011.00302.x
Sipma, K. D., Cornillie, P., Saulez, M. N., Stout, T. A., Voorhout, G., & Back, W. (2013). Phenotypic characteristics of hydrocephalus in stillborn Friesian foals. Veterinary Pathology, 50, 1037-1042. doi: 10.1177/0300985813488955
Ducro, B. J., Schurink, A., Bastiaansen, J. W., Boegheim, I. J., Steenbeek, F. G., Vos-Loohuis, M., Nijman, I.J., Monroe, G.R., Hellinga, I., Dibbits, B.W., Back, W., & Leegwater, P. A. (2015). A nonsense mutation in B3GALNT2 is concordant with hydrocephalus in Friesian horses. BMC Genomics, 16(1). doi: 10.1186/s12864-015-1936-z