Breeds Affected: Pit Bull Terrier
Samples Accepted: Blood, Buccal Swabs
Disease Information: Cone-Rod Dystrophy 2, also known as crd2, is a disease in which the cone and rod cells in the retina degenerate, leading to blindness. Clinical signs can be seen as early as 3 weeks of age, and full blindness results in early adulthood.
Inheritance Information: Crd2 is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The dog is normal, and cannot produce affected offspring.
N/crd2 The dog is a carrier, and can pass the allele on to approximately 50% of any offspring. If bred to another N/crd2 carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
crd2/crd2 The dog is affected. If bred to a normal animal, 100% of the offspring will be carriers. If bred to an N/crd2 carrier, 50% of the offspring will be carriers and 50% will be affected.
– Carriers may be bred to normal animals (N/crd2 x N/N) without any risk of producing affected offspring. The offspring should be tested before breeding to determine if they are carriers or normal.
– Breeding two carriers (N/crd2 x N/crd2) is not recommended due to the possibility of 25% of the offspring being affected.
– Affected animals (crd2/crd2) should not be used for breeding.
Test Information: This mutation test identifies a single base pair insertion in exon 10 of the IQCB1 gene.
Goldstein, O., Mezey, J.G., Schweitzer, P.A., Boyko, A.R., Gao, C., Bustamante, C.D., Jordan, J.A., Aguirre, G.D., Acland, G.M.: IQCB1 and PDE6B mutations cause similar early onset retinal degenerations in two closely related terrier dog breeds. Invest Ophthalmol Vis Sci 54:7005-19, 2013. Pubmed reference: 24045995. Doi: 10.1167/iovs.13-12915.
Further information is available at the Online Mendelian Inheritance in Animals website.