CNGB1 was selected as the most promising positional candidate gene because of its location within the CFA2 region and of the similarity of the phenotype of CNGB1 retinal dystrophy in mice and humans to that of the PRA-affected Papillons in our breeding colony (early lack of rod function and yet a slow retinal degeneration). The gene discussed is CNGB1; the disease is inherited retinal dystrophy.