Cone-Rod Dystrophy 2 (crd2 Dog)

Cone-rod dystrophy 2 (crd2) is an eye disease in which the cones and rods of the retina degenerate. Clinical symptoms usually appear within the first 3 weeks of life and lead to total blindness in early adulthood.

The disease occurs in the American Pit Bull Terrier. The inheritance is autosomal recessive.

Symptoms

Loss of visual acuity
Total blindness in early adulthood

General Information

The disease is caused by the degeneration (dystrophy) of the photoreceptor cells.
First the cones (focused vision/colour vision) in the centre of the retina begin to degenerate.
Later the rods (twilight vision/vision in low light) in the outer area of the retina are affected as well.
Clinical symptoms usually appear within the first 3 weeks of life.

Breeds affected

Pit Bull Terrier, a dog breed affected by cone-rod dystrophy 2 (CRD2)

American Pit Bull Terrier

Test Information

This mutation test detects an insertion of a single base pair (c.952_53insC) in exon 10 of the IQCB1 gene.

Genotype and Lab Report

Inheritance: autosomal recessive

→ The disease only occurs if both alleles of the gene are affected by the mutation (crd2/crd2). Dogs that have only one allele with the causative mutation (N/crd2) are clinically healthy carriers.

Genotypes:

N/N = genetically normal

The dog has no predisposition for crd2 and therefore cannot pass it on to its offspring.

N/crd2 = a carrier

The dog is a clinically healthy carrier. The variation is passed on 50% to the offspring, which are then also carriers.

crd2/crd2 = affected

The variation is passed on 100% to the offspring. The offspring are carriers or affected.

Recommendations

Carrier animals can be bred to normal animals (N/crd2 x N/N). Before breeding with the offspring, it should be tested whether they are normal or carriers.
Mating two carrier animals (N/crd2 x N/crd2) should be avoided because there is a 25% chance that the offspring will be affected.
Affected animals (crd2/crd2) should be excluded from breeding.

Literature

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 Online Mendelian Inheritance in Animals.