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Hydrocephaloid
| Acronym: | HYC |
| Gene: | B3GALNT2 |
| Mutation: | c.1423C>T |
| Inheritance: | Autosomal Recessive |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
| Method: | Sanger sequencing |
Genetics and characteristics
Hydrocephaloid is an inherited brain disease that affects numerous breeds of horses. Horses with hydrocephaloid accumulate cerebrospinal fluid in the brain ventricles, resulting in a marked increase in cranial cavity volume. The disease occurs because of an abnormal narrowing of the opening at the skull base, often leading to death at birth. Hydrocephaloid is caused by a genetic mutation in the beta-1,3-N-acetylgalactosaminyltransferase 2 (B3GALNT2) gene responsible for glycosylation of proteins so they can bind extracellular proteins with greater affinity. The nonsense mutation in the B3GALNT2 gene doesn’t allow for the full-length protein to be produced, which compromises its normal glycosylation function.
Hydrocephaloid is inherited as an autosomal recessive trait, meaning that affected horses have two copies of the mutation. Horses homozygous for the mutation show clinical signs of the disease and are often stillborn or euthanized shortly after birth. Hydrocephaloid affects several breeds of horses, including Quarter Horse, Miniature Horse, Friesian Horse, Standardbred, and Thoroughbred. The disease is incurable, but early detection by genetic testing can help make the correct diagnosis, but even more in a careful selection of mating pairs to avoid further breeding of affected horses.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Ayala-Valdovinos, M. A., Galindo-García, J., Sánchez-Chiprés, D., & Duifhuis-Rivera, T. (2017). Genotyping of friesian horses to detect a hydrocephalus-associated c.1423C>T mutation in B3GALNT2 using PCR-RFLP and PCR-PIRA methods: Frequency in stallion horses in México. Molecular and Cellular Probes, 32, 69–71. doi:10.1016/j.mcp.2016.12.005
Kolb, D.S., Klein, C. (2019). Congenital hydrocephalus in a Belgian draft horse associated with a nonsense mutation in B3GALNT2. Canadian Veterinary Journal 60:197-198, 2019. Pubmed reference: 30705458.