Genetic basis of Congenital Stationary Night Blindness - it is a rare autosomal recessive inherited retinal disorder documented in certain dog breeds, including the Briard and Beagle. The condition is caused by mutations affecting genes involved in retinal signaling and photoreceptor pathway function. Notably, a 1 base pair deletion in the LRIT3 gene has been identified in a research colony of Beagles with CSNB. LRIT3 plays a critical role in the function of the ON-bipolar cells, which transmit signals from photoreceptors to the brain. Mutations in LRIT3, as well as in other genes such as NYX, GRM6, and CACNA1F, have been associated with CSNB in dogs and humans. Dogs affected with CSNB inherit two copies of the mutant gene—one from each parent—to manifest the disease. Carriers with one copy are clinically normal but can pass the mutation to offspring. Genetic testing exists for some forms of CSNB.
Pathophysiology - CSNB is caused by dysfunction in retinal signaling pathways, most notably involving ON-bipolar cells (secondary retinal neurons). This disrupts the retina’s ability to process and transmit signals from photoreceptors, particularly under low-light (scotopic) conditions, leading to loss of night vision. Clinically, night blindness is first observed as early as 5 weeks of age, while anatomical eye changes are generally not detectable until around 2 to 3 years of age. One hallmark ophthalmic finding is the presence of light brown patches on the retinal surface, which enlarge and coalesce over time until they may involve the entire retina. Over time, affected dogs lose not only night vision but may also progressively lose day vision.
Complications - Loss of night vision (nyctalopia) is the earliest symptom, often noted by reluctance to move in low light or at night. Retinal changes become visible in later life (~2–3 years) as brown patches on the retina that increase in size and merge. Progressive vision loss eventually affects day vision as well, leading to partial or complete blindness. Despite visual impairment, eyes are typically not painful unless secondary pathology occurs.
Why This Matters to Breeders and Vets
Breeders: Due to its autosomal recessive inheritance, DNA testing to identify carriers and affected dogs is critical to prevent producing affected litters while maintaining genetic diversity. Breeding two carriers risks 25% affected puppies.
Veterinary Role: Early recognition of night blindness symptoms in puppies and genetic testing where available aid diagnosis. Ophthalmic examination may not reveal retinal changes until later stages, so clinical suspicion is vital.
Management: There is currently no treatment to reverse CSNB. Supportive care and environmental adaptations can help affected dogs navigate safely despite impaired vision.
Research Significance: The canine CSNB model, especially LRIT3-related, has translational potential for understanding similar human conditions and developing targeted therapies.
Summary - Congenital Stationary Night Blindness (CSNB) in dogs is a rare, inherited autosomal recessive retinal disorder characterized by early onset night blindness (from about 5 weeks) with late-appearing retinal lesions visible around 2–3 years of age. Progressive degeneration of retinal ON-bipolar cell function leads to worsening vision, eventually affecting day vision. Genetic mutations, particularly in the LRIT3 gene, cause the disease in some breeds, such as Beagles. Genetic testing and early clinical recognition are essential for responsible breeding and management, although no curative treatment currently exists.