# Discovery of Four New FGF5 Variants Causing Long Hair in the Dog

## TL;DR

Researchers found four new genetic variants in the FGF5 gene that cause long hair in dogs, expanding our understanding of this trait.

## Contribution

The study identifies four novel FGF5 variants associated with the long-hair phenotype in dogs, including in Tibetan Mastiffs.

## Key findings

- Twenty-two Tibetan Mastiffs and one mixed-breed dog with long hair lacked known FGF5 variants but had new ones.
- Four new FGF5 variants were discovered and inherited in a Mendelian pattern, contributing to the long-hair phenotype.
- Some Tibetan Mastiff dogs carried three FGF5 variants, suggesting complex genetic interactions for the long-hair trait.

## Abstract

The long-hair phenotype in dogs is a recessive trait and is caused by five known variants in the FGF5 gene. During a standard genotyping procedure, twenty-two Tibetan Mastiffs and one mixed-breed dog were classified as short-haired, even though they phenotypically clearly showed a long hair phenotype. Re-analysis of their genotype data showed these dogs did not have two known long hair variants. However, it was discovered that these dogs contained other variants in the coding sequence of FGF5. The new variants were inherited in a Mendelian fashion, and dogs with only two putative new variants exhibited the long-hair phenotype, showing these new alleles, together with known variants, can predict the long-hair phenotype.

The long hair phenotype of the dog is ascribed to variants in the fibroblast growth factor 5 (FGF5) gene. Currently, there are five variant alleles known, Lh1 through Lh5, with any combination of these alleles resulting in a long-haired phenotype in dogs. Recently, genotyping of several long-haired dogs for the known Lh1–Lh5 variants yielded unexpected results as these dogs contained no or only one variant in the FGF5 gene known to result in the long-hair phenotype. Analysis of the coding region for the FGF5 gene identified four novel variants associated with the long-haired phenotype. One dog of mixed ancestry had an insertion of G very similar to and near to the long-hair variant Lh4, NC_006614.4: g.37352832insCC. A group of 24 Tibetan Mastiffs showed the Lh1 variant NC_006614.4:g.37372096C>A in 11 dogs only, and no other known Lh variant. Within the coding frame of the FGF5 gene, three unknown variants were discovered that were predicted to have a phenotypic effect. These new variants were inherited in a Mendelian fashion and, in combination with one of the known FGF5 alleles, likely predict the long-hair phenotype. Lastly, eight of the 24 Tibetan Mastiff dogs carried three FGF5 variants.