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Friesian Dwarfism (FD Horse)

Frisian dwarfism (FD) causes abnormal growth of the legs and chest, resulting in severe health problems. The disease is inherited autosomal recessively.


Genetic Test: Currently not available (Contact us for more information.)


  • 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

General Information

  • Abnormal development of legs and rib cage.
  • Affected horses have a normal sized head and torso but unproportional 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.

Breeds affected


Test Information

This test detects the change of a single basepair (c.50G>A) in the B4GALT7 gene.

Genotype and Lab Report

Inheritance: autosomal recessive

→ Only horses with two copies of the variant (fd/fd) are affected. Horses with only one copy (N/fd) are clinically healthy carriers.




N/N = normal

The horse has no copies of the genetic variant causitive for FD and therefore cannot pass it on to its offspring.


N/fd = a carrier

The horse is clinically healthy.  It has one copy of the genetic variant causitive for FD, which will be passed on to its offspring with a probability of 50%.


fd/fd = affected

The horse is affected and has two copies of the genetic variant causitive for FD.  The variant will be passed on to its offspring with a probability of 100%. All offspring will be carriers.


  • 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.

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