Dwarfism - Friesian Horse
A genetic condition in Friesian horses results in a disproportionate form of dwarfism. This form of dwarfism is characterized by abnormally short limbs while the size of the head and length of back are normal. Affected foals also suffer from flexor tendon laxity. Unlike normal foals that grow out of this as they mature, horses impacted by this form of dwarfism continue to be impacted by the condition often resulting in an abnormal gait.
Researchers in the Netherlands identified a mutation (c.50G>A) in exon 1 of the Beta-1,4-Galactosyltransferase 7 (B4GALT7) that is associated with this disorder. B4GALT7 plays an important role in proper formation of extracellular matrix, a key element for bone development. The impact of the mutated gene affects normal collagen and bone development in the affected areas of the body.
Dwarfism in Friesian horses is inherited as a simple autosomal recessive trait. This means that the disorder is not sex linked and all affected foals must inherit two copies of the defective gene (one from each parent). Testing shoes that roughly 12% of the Friesian horse population carriers the mutated gene.
Testing for this form of Dwarfism is valid for Friesian horses and horses with Friesian ancestry.
Additional Tests For Friesian Horses:
Animal Genetics offers DNA testing for a form of Dwarfism found in Friesian horses. The genetic test verifies the presence of the G>A mutation and presents results as one of the following:
|D/D||Affected||The horse carries two copies of the mutation and is homozygous for Dwarfism. The horse is affected.|
|N/D||Carrier||Both the normal and mutant alleles were detected. Horse tested heterozygous for Dwarfism and is a carrier of the mutation associated with your breed.|
|N/N||Clear||Horse tested negative for Dwarfism and does not carry the gene mutation. The horse will not pass on the defective gene to its offspring.|
Leegwater P.A., Vos-Loohuis M., Ducro B.J., Boegheim I.J., van Steenbeek F.G., Nijman I.J., Monroe G.R., Bastiaansen J.W., Dibbits B.W., van de Goor L.H., Hellinga I., Back W. & Schurink A. (2016) Dwarfism with joint laxity in Friesian horses is associated with a splice site mutation in B4GALT7. BMC Genomics 17: 839. doi 10.1186/s12864-016-3186-0.