Testing of dogs: CNGA1-PRA

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PRA in Shelties

Progressive Retinal Atrophy (PRA) is a general name for a group of inherited degenerative diseases of the retina. The retina consists of two types of photoreceptor cells – rods and cones. Rod cells respond only to differences in light intensity and detect black, white and shades of grey and are very sensitive and enable vision in dim light.  The cone cells are responsible for colour vision.

Due to insufficient supply of blood to the retina the photoreceptors of the retina degenerate which usually results in visual impairment and eventually blindness. The disease has been identified in the majority of dog breeds, in wolfs and in humans as well. The disease is genetically heterozygous. This means that it can be caused by different mutations and the symptoms may differ in various dog breeds. Different types of PRA have already been connected with at least 22 mutations in 19 genes. Other types of PRA are distinguished by the age of the disease onset and the rate of progression.

The PRA starts by degeneration and loss of rod cells leading to so-called night blindness. It is followed by cone degeneration which is connected with visual impairment at bright light. PRA in Shelties is clinically indistinguishable from PRA in other dog breeds. The range of the age of the disease onset is relatively wide and in average the first signs of PRA become apparent at the age of 5 years.

In Shelties, the PRA is connected with the mutation in CNGA1 gene. The CNGA1 gene is expressed in the outer segment of the rod photoreceptors of the retina where it takes part in phototransduction. The mutation in this gene causes equivalent disease in humans, the retinitis pigmentosa. In Shelties, the PRA is caused by 4bp deletion in exon 9 (c.1752_1755delAACT) of CNGA1 gene. The mutation leads to reading frame shifting and creation of premature stop codon during the synthesis of CNGA1 protein.

The mutation is inherited autosomal recessively which means that is becomes expressed only in dogs that inherited one mutant allele from both parents (recessive homozygote). A heterozygous individual inherited the mutant allele only from one of its parents and shows no signs of the disease and is considered clinically healthy, however, can pass the mutant allele to its offspring.

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Reference:

A. C. Wiik, E. O. Ropstad, B. Ekesten, L. Karlstam, C. M. Wade and F. Lingaas: Progressive retinal atrophy in Shetland sheepdog is associated with a mutation in the CNGA1 gene; 2015 Stichting International Foundation for Animal Genetics, 46, 515–521

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Usual turnaround time: 7 business days
1 test price: 52.00 $ without VAT