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, NC₀06614. 4: g. 37352832insCC. A group of 24 Tibetan Mastiffs showed the Lh1 variant NC₀06614. 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.
Everts et al. (Tue,) studied this question.