Oculoskeletal dysplasia (OSD) is an inherited disease characterised by skeletal and ocular defects. Skeletal defects include disproportionate shortlimbed dwarfism (short appendages with a normal trunk/body) and skeletal dysplasia (retarded or deformative bone growth. Ocular defects consist of combinations of corneal opacities, enlarged globes, cataract formation, vitreous, optic nerve and retinal abnormalities. The skeletal and ocular abnormalities are visible from a very young age (< 3 months). The ocular defects progress in severity, resulting in loss of vision and eventually blindness.
The single nucleotide substitution in the gene called COL9A3 that causes oculoskeletal dysplasia (OSD1) in Northern Inuits is recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop OSD1 during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop OSD1 as a result of the COL9A3 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop OSD1 should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the COL9A3 mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with OSD1, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.