Genetic basis of Achromatopsia in Shepherd and Arctic breeds - is most commonly caused by a large genomic deletion affecting the CNGB3 gene. This deletion is about 404,820bp in size and identical across these breeds, indicating a founder effect. The condition is inherited in an autosomal recessive manner: dogs must have two copies of the mutated allele to be affected, while carriers have only one copy and show no symptoms. Genetic testing can accurately identify affected, carrier, and clear individuals regardless of age.
Pathophysiology - The CNGB3 gene encodes the beta subunit of the cyclic nucleotide-gated channel critical for cone photoreceptor function. The deletion leads to degeneration and dysfunction of the cone photoreceptors, resulting in the loss of color vision and severe day blindness (hemeralopia). Vision in dim light remains normal due to rod photoreceptor preservation. Symptoms usually appear as early as 8-12 weeks of age, with affected dogs avoiding bright light and showing impaired vision in daylight.
Complications - Affected dogs experience day blindness, color blindness, and may display photophobia (light sensitivity). Behavioral changes, such as avoidance of bright daylight and increased activity at twilight or night, are common. Routine eye exams generally do not detect achromatopsia, making genetic testing vital for diagnosis.
Why This Matters to Breeders and Vets - For breeders: Genetic testing allows selection against carrier matings, reducing the risk of producing affected puppies. This is especially important in breeds where the deletion is known to be present. For veterinarians: Awareness of the disease, its symptoms, and the need for genetic confirmation helps differentiate achromatopsia from other vision disorders and helps advise on management strategies (such as minimizing bright light exposure). Knowing the inheritance and breed prevalence supports responsible breeding and overall canine welfare.
Summary - Achromatopsia (Shepherd/Arctic Breed Type) is an autosomal recessive disorder most often caused by a large, identical-by-descent deletion in the CNGB3 gene. It results in cone photoreceptor degeneration and severe day blindness but spares rod function, so affected dogs can see well in dim light. Genetic testing is essential for diagnosis, prevention, and management, and is especially relevant for breeders and veterinarians working with arctic and shepherd breeds.