Genotypic Distribution of FGF4L2 in DTK-Registered Dachshunds in Germany: A Pilot Study

Background/Objectives: The fibroblast-growth-factor 4 retrogene insertion on chromosome 12 (FGF4L2) is known to be associated with chondrodystrophy and intervertebral disc disease (IVDD), which increases the risk of Hansen’s type I intervertebral disc extrusion (IVDE) in Dachshunds. While the FGF4L2 insertion is known to occur at high frequency within the breed, subgroup-specific data relating to coat-type and size categories remain limited. This pilot study aimed to determine the distribution of FGF4L2 and wild-type (N) alleles in a cohort of Dachshunds registered with the German Dachshund Club (DTK) and to evaluate differences among coat and size varieties. Methods: A total of 488 Dachshund samples from the DNA archive of the Deutscher Teckelklub 1888 e.V. (DTK) were analysed and genotyped. Genotype data was categorised according to coat-type and size variant. Allele and genotype frequencies were calculated for the overall population and for each subgroup. Results: The overall frequency of the FGF4L2 insertion allele was 96.51% (95% CI: 95.17–97.50). However, there were moderate differences between subgroups. The allele was nearly fixed in several coat and size variants. Standard wire-haired Dachshunds had the lowest allele frequency (89.09%) and were the only group in which homozygous wild-type individuals were observed. Heterozygous frequencies peaked in standard smooth-haired (16.7%) and standard wire-haired (14.5%) groups. Conclusions: Because the FGF4L2 frequency differs meaningfully between Dachshund varieties, grouping them into a single breed, as many studies do, can obscure the residual subgroup-specific genetic variation present in this population. Analysing the varieties separately provides a basis for future studies investigating factors that may interact with FGF4L2 in IVDE, thereby highlighting its multifactorial nature. It also reveals where wild-type alleles persist, making genotype-informed, variety-specific breeding a viable strategy for improving vertebral column health. However, variation in FGF4L2 allele frequency alone may not fully account for the recently reported differences in vertebral column health between Dachshund coat varieties.