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Dwarfism Friesian Horse Type
| Acronym: | DFHT |
| Gene: | B4GALT7 |
| Mutation: | c.50G>A |
| Inheritance: | Autosomal Recessive |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
| Method: |
Genetics and characteristics
Dwarfism Friesian horse type is an inherited growth disease that affects the Friesian breed of horses. Friesian horses with dwarfism have retarded growth of limbs and ribs, while the size of the head and the length of the back are normal. The affected horses exhibit hyperextension of fetlock joints of all limbs with varying degrees of severity. Dwarfism Friesian horse type is caused by a genetic mutation in the xylosylprotein beta 1,4-galactosyltransferase, polypeptide 7 (B4GALT7) gene responsible for proper formation of the extracellular matrix, crucial for bone development. The missense mutation in the B4GALT7 gene causes impairment of gene function, which interferes with adequate collagen formation, essential in bone development.
Dwarfism Friesian horse type is inherited as an autosomal recessive trait; therefore, two copies of the mutation are needed for a horse to be affected, and the disease occurs in males and females. This type of dwarfism affects only the Friesian horse breed. The disease is incurable, but early detection by genetic testing can help identify horses that are carriers of the disease and prevent further breeding by mating pairs selection.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Leegwater, P. A., Vos-Loohuis, M., Ducro, B. J., Boegheim, I. J., van Steenbeek, F. G., Nijman, I. J., … Schurink, A. (2016). Dwarfism with joint laxity in Friesian horses is associated with a splice site mutation in B4GALT7. BMC Genomics, 17(1). doi:10.1186/s12864-016-3186-0
Orr, N., Back, W., Gu, J., Leegwater, P., Govindarajan, P., Conroy, J., … Brama, P. A. J. (2010). Genome-wide SNP association-based localization of a dwarfism gene in Friesian dwarf horses. Animal Genetics, 41, 2–7. doi:10.1111/j.1365-2052.2010.02091.x