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→ Dwarfism in the Friesian breed with disproportionate limbs.
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- Abnormal development of leg bones and rib cage.
- Affected horses have a normal sized head and torso but disproportionately short legs.
- Rib cage shows inward protrusion of ribs which may lead to breathing issues.
- Tendon laxity leads to instable joints and hence to abnormal gait.
- Short legs in comparison to a normal sized head and torso
- Inward protruded rib cage
- Hyperextension of fetlock joints
- Tendon laxity
- Abnormal gait with outward rotation
Inheritance and Genotypes
→ Friesian Dwarfism is an autosomal recessive hereditary disease, meaning that horses with only one copy of the genetic variant (N/fd) are clinically normal carriers while horses with two copies of the genetic variant (fd/fd) are affected.
|Genotype:||The horse is:||Effects:|
|N/N||normal.||The horse does not have any copies of the genetic variant causative for Friesian Dwarfism and therefore cannot pass it on to any offspring.|
|N/fd||a carrier.||The horse is clinically healthy. It has one copy of the genetic variant causitive for Friesian Dwarfism, which will be passed on to its offspring with a probability of 50%.|
|fd/fd||affected.||The horse has two copies of the genetic variant causitive for Friesian Dwarfism. The variant will be passed on to all offspring. All offspring will be carriers (N/fd).|
- Carriers may be bred to normal animals (N/fd x N/N) without any risk of producing affected offspring. The offspring should also be tested before breeding to determine if they are carriers or normal.
- Breeding two carriers (N/fd x N/fd) is not recommended due to the possibility of 25% of the offspring being affected.
- Affected animals (fd/fd) should not be used for breeding.
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. : Dwarfism with joint laxity in Friesian horses is associated with a splice site mutation in B4GALT7. BMC Genomics 17:839, 2016. Pubmed reference: 27793082. DOI: 10.1186/s12864-016-3186-0.
Further information is available Online Mendelian Inheritance in Animals.