Genetic basis of Achromatopsia in Labrador Retrievers - is caused by a recessive mutation in the CNGA3 gene, specifically a deletion of three base pairs in exon 7 (c.1931_1933del). This gene encodes the alpha subunit of a cyclic nucleotide-gated ion channel, crucial for cone photoreceptor signal transmission. The disease is inherited in an autosomal recessive manner: only dogs homozygous for the mutation (achm2/achm2) are affected, while heterozygous dogs (N/achm2) are healthy carriers. Genetic testing can differentiate between affected, carrier, and clear individuals at any age.
Pathophysiology - Achromatopsia results from degeneration and dysfunction of cone photoreceptors, which are responsible for color and high-acuity vision. The CNGA3 mutation disrupts cellular signaling needed for normal cone function, causing cones to lose their ability to respond to light properly. Impacted dogs develop day blindness (hemeralopia)—severely impaired vision in bright daylight—since rod photoreceptors (responsible for low-light vision) remain functional, but cones do not.
Complications - Vision loss in bright light: Affected puppies may show signs as early as 8-12 weeks, including day blindness, photophobia (painful light sensitivity), and color blindness. Behavioral changes: Puppies may avoid bright daylight and are more active during twilight or at night. Potential misdiagnosis: Routine eye exams may not detect achromatopsia, so genetic testing is recommended for confirmation.
Why This Matters to Breeders and Vets - Breeders: Knowledge of carrier status is critical to prevent breeding two carriers, which results in 25% affected, 50% carriers, and 25% clear offspring per litter on average. This preserves vision and animal welfare and avoids producing puppies with day blindness. Vets: Early awareness allows for advice to owners on managing photophobia (such as using tinted lenses, avoiding bright light, and modifying routines). Welfare: Preventative genetics help maintain breed health and avoid behavioural problems due to vision loss.
Summary - Achromatopsia (Labrador Type) is a recessive disorder resulting from a mutation in the CNGA3 gene, leading to cone degeneration and day blindness in affected dogs. Genetic testing enables breeders to avoid producing affected puppies, protecting both animal health and breeder reputation. Veterinarians can guide owners in managing the condition and distinguishing it from other retinal diseases.