Absence of FGF4 Retrogene Insertion on Chromosome 18 Results in a Tall Phenotype in Grand Basset Griffon Vendéen Dogs

Every dog breed has characteristic physical features that have been fixed through numerous generations of selective breeding. For the Grand Basset Griffon Vendéen (GBGV) breed, short-leggedness has been established as the breed standard. Although breeders have been consistent in only breeding dogs that meet this standard, occasionally litters have included dogs that are significantly taller. In many dog breeds short leg length is associated with insertion of an <i>FGF4</i> retrogene (<i>FGF4RG</i>) at specific sites on either chromosome 12 (<i>12-FGF4RG</i>) and/or 18 (<i>18-FGF4RG</i>). A study was undertaken to determine whether <i>FGF4RG</i> genotype is the basis of the height difference. Of 47 GBGVs that were evaluated, 41 had leg lengths within the breed standard and 6 were significantly taller. None of the dogs had the <i>12-FGF4RG</i> insertion. The short-legged dogs were either homozygous or heterozygous for the <i>18-FGF4RG</i> insertion. All six long-legged dogs were homozygous for the non-insertion allele. This indicates that selective breeding based on phenotype alone has not been sufficient to fix short-leggedness in the breed due to retention of the non-insertion allele. The finding that one copy of the insertion is sufficient to confer short-leggedness indicates that expression of the retrogene during development is likely to inhibit growth of the limbs.