Genetic basis of Early-Onset Progressive Retinal Atrophy - is caused by mutations in specific genes such as PDE6B, among others, depending on the breed. EOPRA is inherited in an autosomal recessive pattern, meaning two copies of the mutated gene are required for the disease to manifest. For example, in Portuguese Water Dogs and Spanish Water Dogs, EOPRA is caused by mutations in the PDE6B gene. More than 20 mutations in different genes have been associated with various forms of PRA in dogs, many being breed-specific
Pathophysiology - EOPRA leads to degeneration of the photoreceptor cells in the retina, starting early during or soon after retinal development. This progressive degeneration results in a gradual loss of rod and cone cells, which are essential for vision in low light and daylight, respectively. Loss of function leads to visual impairment that progresses to complete blindness.
Complications - Progressive blindness leads to disorientation, increased risk of injury, and reduced quality of life. Secondary complications such as cataracts may develop. No cure currently exists; management focuses on support and environmental modification.
Clinical Presentation - Usually presents at a young age, often from about 1.5 to 3 years old. Early signs include night blindness or difficulty seeing in dim light, progressing to complete vision loss. Ophthalmic exams reveal retinal degeneration, including retinal thinning, tapetal hyper-reflectivity, and vascular attenuation. Dogs initially compensate well but show worsening vision over time
Inheritance - Autosomal recessive inheritance: affected dogs have two copies of the defective gene. Carriers have one copy and do not show symptoms but can pass the gene to offspring. Both sexes are equally affected.
Why This Matters to Breeders and Vets - causes irreversible blindness, impacting quality of life. Genetic testing allows early identification of carriers and affected dogs to avoid breeding affected puppies. Early diagnosis through testing can lead to earlier management and owner education.