Oculoskeletal dysplasia (OSD, drd1) of the Labrador retriever, combining disproportionate short-limb dwarfism (especially forearms) with vitreous and retinal dysplasia progressing to retinal detachment and cataracts. It is recessively inherited and due to mutations in COL9A3. Heterozygous carriers may show mild ocular signs (focal retinal folds, vitreous filaments), so phenotypically healthy breeding animals should also be tested.

Specific to the Labrador retriever (drd1 locus). The population frequency of the variant in the Labrador is not firmly established. In the Northern Inuit Dog, the allele frequency is 0.08 (carriers ~15%).

- Disproportionate dwarfism with short limbs (especially radius and ulna, curved with varus/valgus deformity)\n- Prominent cranial vault and moderate exotropic strabismus\n- Vitreous dysplasia and vitreous filaments\n- Retinal folds and retinal dysplasia plaques\n- Retinal detachment and congenital or juvenile cataracts\n- Mild ocular signs possible in heterozygous carriers

Carrig and colleagues described in 1977 the association between retinal dysplasia and skeletal dysplasia in the Labrador retriever, and Farnum and colleagues characterized in 1992 ocular chondrodysplasia with morphometric analysis. Goldstein and colleagues (2010), through candidate locus analysis in the region mapped on canine chromosome 24, identified a single-base insertion in exon 1 of COL9A3 that produces a frameshift and a premature stop codon in the COL3 domain of the alpha-3(IX) collagen chain. In the Samoyed, a clinically similar form (drd2) is due to a 1,267 bp deletion at the 5' end of COL9A2. COL9A3 expression is reduced in affected retinas.

- Test breeding animals before mating with the Labrador-specific COL9A3 (drd1) test\n- Do not cross two carriers: 25% risk of affected homozygotes\n- A carrier can be mated with a free individual; offspring intended for breeding must be tested (also if phenotypically healthy)\n- Monitor ocular signs in breeding animals: vitreous filaments or retinal folds may indicate a heterozygous carrier\n- Distinguish from SD2 (COL11A2) and from other skeletal dysplasias of the Labrador: the molecular test is decisive

The differential diagnosis includes multifocal retinal dysplasia (MFRA) and other PRAs of the Labrador, as well as other chondrodysplasias of the breed. Confirmation by genetic testing is essential because the ocular signs of heterozygous carriers are subtle. In a Labrador with juvenile retinal detachment and skeletal signs, OSD should be the first suspicion. In the Samoyed, the equivalent form (drd2) is due to COL9A2, not COL9A3.

1. Goldstein O, et al. COL9A2 and COL9A3 mutations in canine autosomal recessive oculoskeletal dysplasia. Mamm Genome. 2010;21(7-8):398-408. PMID: 20686772
2. Stavinohova R, et al. Clinical, histopathological and genetic characterisation of oculoskeletal dysplasia in the Northern Inuit Dog. PLoS One. 2019;14(8):e0220761. PMID: 31415586