PRA-rcd3 in Cardigan Welsh Corgi, Pomeranian and Chinese Crested dog

Progressive retinal atrophy (PRA) is a name for group of disease with similar clinical manifestation.

In Cardigan Welsh Corgi, Pomeranian and Chinese Crested dog breeds, an early onset PRA was found. This form of PRA disease is called rcd3 = rod cone dysplasia type 3.

Retina consists of two types of photoreceptor cells:

• Rods are more photosensitive, they differentiate gray scale colours, they allow night vision.
• Cones intermediate colour perception.

By PRA-rcd3 disease, retinal photosensitive cells (rods and cones) are not well supplied with blood and so they are gradually dying off. An affected individual becomes usually blind in very early age. Rcd3 is a cureless disease.

PRA-rcd3 disease was first described in 1972 in Australia - affected dog had been imported from Great Britain. Since that, rcd3 disorder has been extended in to whole world.

PRA-rcd3 is caused by single adenine deletion in c.1847del of PDE6A gene (a-subunit of cyclic guanosine monophosphate (cGMP) phosphodiesterase). The deletion incurs a frame shift and forming of premature stop codon during PDE6A synthesis.

PRA-rcd3 in Cardigan Welsh Corgi and Chinese Crested dog is an autosomal recessive disorder. The disease affects dogs with homozygous genotype only (positive / positive). Dogs with heterozygous genotype (positive /negative) are clinically without any symptoms. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % healthy non-carriers, 25 % affected homozygotes, and 50 % healthy carriers. Because of high risk of producing affected offspring, mating of two carriers can not be recommended.

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Thanks to Petersen-Jones SM from College Of Veterinary Medicine at Michigan State University who helped us validate testing method.

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References:

Louise M. Downs, Rebekkah Hitti, Silvia Pregnolato and Cathryn S. Mellersh: Genetic screening for PRA-associated mutations in multiple dog breeds shows that PRA is heterogeneous within and between breeds; Veterinary Ophthalmology (2014) 17, 2, 126–130

Petersen-Jones SM, Entz DD, Sargan DR: cGMP Phosphodiesterase-a Mutation Causes Progressive Retinal Atrophy in the Cardigan Welsh Corgi Dog; IOVS, July 1999, Vol. 40, No. 8

Petersen-Jones SM, Entz DD: An improved DNA-based test for detection of the codon 616 mutation in the alpha cyclic GMP phosphodiesterase gene that causes progressive retinal atrophy in the Cardigan Welsh Corgi; Veterinary Ophthalmology (2002) 5, 2, 103-106