Progressive Retinal Atrophy (crd4-PRA/cord1 and MAP9) – 2 variants

Progressive Retinal Atrophy (PRA) encompasses a group of hereditary retinal diseases that cause gradual vision loss due to degeneration of photoreceptor cells. The crd4-PRA variant, also known as cord1, is primarily found in Dachshunds (especially Miniature Longhaired) and English Springer Spaniels. It is caused by an autosomal recessive mutation in the retinitis pigmentosa GTPase regulator-interacting protein 1 (RPGRIP1) gene.
Recent research has shown that RPGRIP1 alone may not be sufficient to cause disease. A second mutation in the MAP9 gene (microtubule-associated protein 9) acts as a modifier, accelerating disease onset when present alongside RPGRIP1.

Dogs affected by crd4-PRA (cone-rod dystrophy type 4) display a progressive degeneration of both cone and rod photoreceptor cells in the retina, leading to gradual vision loss. Early signs of visual impairment can appear as young as 10 to 12 weeks of age, especially in individuals carrying mutations in both RPGRIP1 and MAP9. Common symptoms include difficulty tracking moving objects, clumsiness, and night blindness. However, the age of onset and severity vary widely: some dogs may be blind by six months, while others retain functional vision well into their senior years. On average, signs of sight loss begin around five years of age. This variability is influenced by genetic modifiers such as MAP9, which can accelerate disease progression when present alongside RPGRIP1 mutations.