Progressive retinal atrophy (crd-PRA)

The crd-PRA (cone-rod dystrophy) is an autosomal recessive inherited photoreceptor disease caused by the predominant loss of cone function. A mutation in the nephronophthisis 4 (NPHP4) gene leads to this form of PRA. The photoreceptor cells of the retina can be divided into rods or cones depending on their function. The rod cells are specialized for the mesopic vision and contrast sensitivity. The cone cells are responsible for color vision. In contrast to rod-cone dystrophies, where firstly, rod cells are affected and secondly, degeneration of the cone cells results in complete blindness of the dog, cone-rod dystrophies are characterised by the relatively early loss of cone photoreceptors while the rod function remains relatively preserved. The disease usually ends with day blindness. The earliest ophtalmoscopic signs appear at about six month of age. The complete manifestation of the diseases (complete day blindness) occur at an age of around 1 to 2.