Because the affected dogs did not share common alleles, we excluded single, fully penetrant mutations in six known canine retinal disease genes: BEST1[8], [9], PDE6B and PDE6A[23]–[26], RPE65[6], [7], NPHP4[28], and CNGB3[29], [30]. Here, PDE6B is linked to Abnormal retinal morphology.