Hydrocephalus (HDC)
Gene or Region: B3GALNT2
Reference Variant: C
Mutant Variant: T
Affected Breeds: Friesian and Other Breeds
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 for Hydrocephalus
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
More Horse Health
Equine Metabolic Syndrome / Laminitis Risk
Equine Metabolic Syndrome (EMS) is a wide-spread issue in the horse population. Primarily characterized by hyperinsulinemia (excess insulin circulating in the blood in relation to glucose levels), this metabolic disorder is often present in obese horses and ponies and can be challenging to diagnose as it can be misdiagnosed as "Cushing's" (a pituitary disfunction).
Equine Recurrent Uveitis Risk and Severity
Equine Recurrent Uveitis (ERU) is the most common cause of blindness in horses, affecting about 3-15% of the horse population worldwide. Characterized by episodes of inflammation of the middle layer of the eye, Equine Recurrent Uveitis in horses leads to the development of cataracts, glaucoma and eventually complete loss of vision.
Foal Immunodeficiency Syndrome
Foal immunodeficiency syndrome (FIS) is a failure in the development of the adaptive immune system. At 3-6 weeks of age, once the maternal antibodies begin to degrade, foals exhibit signs of anemia, diarrhea, and pneumonia. As these foals fail to respond to treatment for infections, they are humanely euthanized at a young age.
Glanzmann Thrombasthenia
Glanzmann Thrombasthenia (GT) is a blood platelet function disorder, resulting from a reduction in the platelet fibrinogen receptor protein. Clinical signs can be characterized by bleeding on the skin or from the mouth/nostril/gastrointestinal mucosas, and may include skin rashes with blood spots under the skin, nasal bleeding, gastrointestinal and gingival bleedings.