Cone-rod dystrophy 3 in Glen of Imaal Terriers

The disease is characterized by dystrophy of the retinal lens cells - the cones (cone), which allow colour  vison and visual acuity, and the rods (rod), which allow vision in dm light. Affected dogs suffer a severe and rapidly progressive loss of cone function, which is accompanied by a relatively slower loss of rod function. The disease leads to a marked deterioration of vision, both in bright and dim light, up to complete blindness.

Cone and rod dystrophy is caused by deletion of exons 15 and 16 in the ADAM9 gene, which alters the reading frame, leading to premature inclusion of the stop codon and removal of a critical domain from the encoded protein.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

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References:

Kropatsch, R., Petrasch-Parwez, E., Seelow, D., Schlichting, A., Gerding, WM., Akkad, DA., Epplen, JT., Dekomien, G.: Generalized progressive retinal atrophy in the Irish Glen of Imaal Terrier is associated with a deletion in the ADAM9 gene. Mol Cell Probes 24:357-63, 2010. Pubmed reference: 20691256