Pathological and electrophysiological features of a canine cone-rod dystrophy in the miniature longhaired dachshund

PURPOSE: To characterize the electrophysiological and histopathological features of a retinal degenerative disease in a colony of miniature longhaired dachshunds known to have a form of progressive retinal atrophy (PRA). METHODS: Serial electroretinograms were recorded from affected homozygous (n = 36) and heterozygous (n = 15) dogs. Morphologic investigations including immunohistochemistry and lectin histochemistry were performed on selected homozygous animals (n = 15). RESULTS: Clinical findings included loss of tapetal hyperreflectivity. The mode of inheritance was autosomal recessive. An early dramatic reduction of cone-specific ERG amplitude with a more modest reduction in rod b-wave amplitude was demonstrated. Progressively, rod specific responses diminished until there were no recordable responses to the ERG stimuli at 40 weeks of age. Morphologic changes confirmed early cone inner and outer segment loss. Other abnormalities included opsin mislocalization and outer nuclear layer thinning due to the subsequent loss of rod photoreceptors. CONCLUSIONS: A novel canine cone-rod dystrophy has been identified.