Genetic basis of Canine multifocal retinopathy - an autosomal recessive inherited disorder caused by mutations in the BEST1 gene (also known as VMD2), which encodes a protein called bestrophin-1. Bestrophin-1 is critical for the normal function of the retinal pigment epithelium (RPE), a layer of cells that supports retinal health and function. Affected dogs inherit two copies of the pathogenic BEST1 mutation—one from each parent—to develop the disease. Carriers with only one mutated copy show no clinical signs but can pass the mutation to offspring.
Pathophysiology - The mutation in the BEST1 gene leads to dysfunction of the retinal pigment epithelium, resulting in fluid accumulation beneath the retina. This causes multiple discrete circular areas of retinal detachment, often described as blister-like lesions due to their raised appearance. These lesions are typically visible on veterinary eye examinations as gray, tan, orange, or pink spots and may vary in number, size, and location. The fluid accumulation and detachment disrupt the normal attachment of the retina to the underlying tissues but usually progress slowly and may stabilize or even partially resolve over time.
Complications - Affected dogs typically present clinically between 11 and 16 weeks of age. The lesions are usually bilateral and multifocal. Although the retinal changes are visible, vision loss is uncommon, and many affected dogs retain normal vision. The retinal lesions generally do not progress after 6 to 12 months of age and in some cases may appear to heal, becoming no longer visible on eye examination. Vision impairment has been reported in rare cases of multifocal retinopathy but is not the norm.
Why This Matters to Breeders and Vets
Inheritance pattern: Because CMR is autosomal recessive, breeding two carriers risks producing affected puppies. Genetic testing for BEST1 mutations allows breeders to identify carriers and make informed breeding decisions to avoid affected litters while maintaining genetic diversity.
Veterinary diagnosis: Early identification via eye examination and confirmation by genetic testing helps differentiate CMR from other retinal diseases and guides prognosis. Veterinarians should be aware of the typical age of onset and clinical signs to advise breeders and owners effectively.
Management: Since vision is usually preserved and progression is slow, the disease often requires no treatment. However, affected dogs should be monitored for any unusual vision changes or complications. Responsible breeding is key to reducing disease prevalence.
Summary - Canine multifocal retinopathy is a genetic eye disorder caused by pathogenic mutations in the BEST1 gene, inherited in an autosomal recessive manner. It manifests between 11 and 16 weeks as multiple circular retinal detachments with underlying fluid accumulation, seen as blister-like lesions on eye exam. These lesions typically stabilize by one year of age and rarely cause significant vision loss. Genetic testing is essential for breeders to prevent producing affected puppies, and veterinarians play a vital role in diagnosis and monitoring.
