Original publication (Mellersh et al., 2006) reported strong association between mutation and disease in an inbred colony of MLHDs. Subsequent publications reported variability in phenotype associated with this mutation in outbred MLHDs and in Expert comments: 2016 Forman et al., reported a second mutation, in MAP9, that modifies the effect of the RPGRIP1 insertion. This, and other studies, showed that MLHDs that are homozygous for the RPGRIP1 mutation alone are affected with a late-onset, slowly progressing cone deficit that doesn't necessarily lead to visual impairment, whereas dogs that are homozygous for the RPGRIP1 and MAP9 mutations suffer from an early onset, rapidly progressing disease. In breeds that segregate the MAP9 mutation, avoiding breeding RPGRIP1 homozygotes is rational because it can be associated with a blinding disease. In breeds that don't segregate the MAP9 mutation, breeding away from the RPGRIP1 mutation may simply serve the purpose of eliminating the late onset, slowly progressing disease. The challenge is that screening for the MAP9 mutation is technically very difficult, due to the nature of the mutation. In the absence of information regarding the segregation of MAP9 in a particular breed it seems prudent to breed away from RPGRIP1 in all varieties of Dachshunds. Mellersh, C. S., M. E. Boursnell, L. Pettitt, E. J. Ryder, N. G. Holmes, D. Grafham, O. P. Forman, J. Sampson, K. C. Barnett, S. Blanton, M. M. Binns and M. Vaudin, (2006) Canine RPGRIP1 mutation establishes cone-rod dystrophy in miniature longhaired dachshunds as a homologue of human Leber congenital amaurosis. Genomics, 88, 293-301.; Miyadera, K., K. Kato, J. Aguirre-Hernandez, T. Tokuriki, K. Morimoto, C. Busse, K. Barnett, N. Holmes, H. Ogawa, N. Sasaki, C. S. Mellersh and D. R. Sargan, (2009) Phenotypic variation and genotype-phenotype discordance in canine cone-rod dystrophy with an RPGRIP1 mutation. Mol Vis, 15, 2287-305.

Original publication (Mellersh et al., 2006) reported strong association between mutation and disease in an inbred colony of MLHDs. Subsequent publications reported variability in phenotype associated with this mutation in outbred MLHDs and in Expert comments: 2016 Forman et al., reported a second mutation, in MAP9, that modifies the effect of the RPGRIP1 insertion. This, and other studies, showed that MLHDs that are homozygous for the RPGRIP1 mutation alone are affected with a late-onset, slowly progressing cone deficit that doesn't necessarily lead to visual impairment, whereas dogs that are homozygous for the RPGRIP1 and MAP9 mutations suffer from an early onset, rapidly progressing disease. In breeds that segregate the MAP9 mutation, avoiding breeding RPGRIP1 homozygotes is rational because it can be associated with a blinding disease. In breeds that don't segregate the MAP9 mutation, breeding away from the RPGRIP1 mutation may simply serve the purpose of eliminating the late onset, slowly progressing disease. The challenge is that screening for the MAP9 mutation is technically very difficult, due to the nature of the mutation. In the absence of information regarding the segregation of MAP9 in a particular breed it seems prudent to breed away from RPGRIP1 in all varieties of Dachshunds. Mellersh, C. S., M. E. Boursnell, L. Pettitt, E. J. Ryder, N. G. Holmes, D. Grafham, O. P. Forman, J. Sampson, K. C. Barnett, S. Blanton, M. M. Binns and M. Vaudin, (2006) Canine RPGRIP1 mutation establishes cone-rod dystrophy in miniature longhaired dachshunds as a homologue of human Leber congenital amaurosis. Genomics, 88, 293-301.; Miyadera, K., K. Kato, J. Aguirre-Hernandez, T. Tokuriki, K. Morimoto, C. Busse, K. Barnett, N. Holmes, H. Ogawa, N. Sasaki, C. S. Mellersh and D. R. Sargan, (2009) Phenotypic variation and genotype-phenotype discordance in canine cone-rod dystrophy with an RPGRIP1 mutation. Mol Vis, 15, 2287-305.