Hydrocephalus (HDC)
Gene or Region: B3GALNT2
Reference Variant: C
Mutant Variant: T
Affected Breeds: Friesian
Research Confidence: High - Identical mutation present in human hydrocephalus
Explanation of Results: hdc/hdc = homozygous for Hydrocephalus, lethal hdc/n = heterozygous for Hydrocephalus, carrier n/n = no variant detected
General Description
Hydrocephalus is an abnormal build up of cerebral spinal fluid around the brain.In the Friesian, it is believed that a narrowing of a passage within the brain prevents normal fluid absorption, leading to an obvious external cranial distension. Affected foals are often stillborn and are associated with dystocia in the dams. Hydrocephalus is an autosomal recessive disorder, thus a foal must inherit two copies of the mutant allele to be affected. Horses with only one copy of the allele are known as carriers due to their ability to produce an affected foal.
Gene Information
B3GALNT2 is an enzyme involved in glycoylation of alpha-dystroglycan. Mutations in this gene result in various human muscular dystrophies, some of which also involve hydrocephalus. The mutation observed in Friesians introduces an early stop codon, resulting in an incomplete (and thus likely non-functional) protein.
References
Ducro BJ et al., “A nonsense mutation in B3GALNT2 is concordant with hydrocephalus in Friesian horses.” (2015) BMC Genomics. 16: 761. PMID: 26452345
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