Turnaround: 3-5 business daysTurnaround: 7-10 business days
Price: $40.00Price: £35.00
Breeds: Appaloosa/Friesian, Arabian/Friesian Cross, Baroque Pinto, Friesian, Friesian Cross, Mixed Breed, Moriesian, Stonewall Sporthorse, Unspecified, Warlander
Description
A genetic condition in Friesian horses causes a disproportionate form of dwarfism. Affected horses have abnormally short limbs and ribs that protrude inward, while head size and back length appear normal. A striking feature of the condition is flexor tendon laxity, which causes hyperextension of the fetlock joints. Normal foals grow out of tendon laxity as they mature, but horses with this form of dwarfism remain affected, often resulting in an abnormal gait.
Researchers in the Netherlands identified the causative variant (c.50G>A) in the beta-1,4-galactosyltransferase 7 (B4GALT7) gene. The variant changes the last nucleotide of exon 1 and disrupts normal splicing of the gene’s RNA. B4GALT7 is needed to build proteoglycans, key components of the extracellular matrix in cartilage and growth plates, and its disruption impairs normal bone growth. Similar B4GALT7 mutations in humans cause a form of Ehlers-Danlos syndrome with growth retardation and joint laxity.
Dwarfism in Friesian horses is inherited as an autosomal recessive trait, so a foal must inherit one copy of the variant from each parent to be affected. Because the condition is not treatable, prevention through breeding is the best way to manage it. Roughly 12% of the Friesian population carries the variant, and DNA screening of breeding stock is the only way to identify carriers and avoid pairings (FD/N x FD/N) that carry a 25% risk of producing an affected foal.
Possible results
| Genotype | Description |
|---|---|
| FD/FD | Affected: Horse has two copies of the Friesian dwarfism variant and is expected to develop signs of the disorder. All offspring will inherit the variant. |
| FD/N | Carrier: Horse has one copy of the Friesian dwarfism variant and is not expected to show signs of the disorder. Each offspring has a 50% chance of inheriting the variant. |
| N/N | Clear: Horse does not carry the Friesian dwarfism variant and cannot pass it on to offspring. |
Breeds Affected
Friesian
Reference
Dwarfism with joint laxity in Friesian horses is associated with a splice site mutation in B4GALT7.
[PMID: 27793082]
Genome-wide SNP association-based localization of a dwarfism gene in Friesian dwarf horses.
[PMID: 21070269]