Curly Coat & Hypotrichosis Horse

Curly Coat & Hypotrichosis

A curly coat in horses, known particularly as the distinctive trait of the American Bashkir Curly Horse, is caused by a complex interaction between two separate genes, KRT25 and the transcription factor SP6. Our CombiBreed DNA test for Curly Coat with or without Hypotrichosis analyses for both the mutation in SP6 as well as in KRT25.

Clinical features

A curly coat in horses presents as short, coarse curls or waves. SP6 and KRT25 can also cause hypotrichosis: a loss of tail and mane hair. Horses with incomplete hypotrichosis, or “scanty tail”, retain some degree of hair growth on their mane and tail. Horses with complete hypotrichosis, or “string tail”, have no mane and a bare tail.

Inheritance

Because the KRT25 and SP6 gene have an epistatic effect on each other, the phenotype is determined by a combination of the alleles on both genes. For each gene, a horse can have 3 possible genotypes, a combination of the inherited alleles from both parents. In KRT25 the normal allele is written as G and the mutant is T. For the SP6 alleles, C is the normal wildtype and T is the mutant allele. Both mutant alleles are at least partially dominant over the normal alleles, and also interact with each other.

A horse with a genotype of G/G + C/C is entirely unaffected and will develop a straight coat with normal thickness. A genotype of G/G + C/T or G/G + T/T causes a curly coat. A genotype of G/A + C/T or G/A + C/C causes curly coat and incomplete hypotrichosis. Finally, a genotype of A/A + C/C causes a curly coat with complete hypotrichosis. Some possible genotypes still have an unknown/unconclusive effect on the phenotype. Therefore, these results have no reported phenotype.

Phenotypes resulting from different KRT25 and SP6 genotypes

Hypoallergic horses?

Although science still debates about this subject, it is sometimes mentioned that curly horses are hypoallergic, meaning that this hair structure could be an alternative for people that are allergic for (most) horses.

Relevant tests

• P331