What is Progressive Retinal Atrophy (PRA?)

Progressive Retinal Atrophy is a group of genetic eye disorders that share similar symptoms and occur in over 100 dog breeds. In dogs suffering from Progressive rod-cone degeneration (PRA-prcd) the cells of the rods and cones in the retina of the eye degenerate when the dog reaches early adolescence. PRA-prcd is diagnosed as a late onset disease as the retina cells develops normally after birth and then starts to degenerate later in life (Acland et al. 1998). Night blindness normally develops at around 2 ? 3 years of age and progresses to complete blindness at around 5 years of age (Andre et al., 2008). Close to 30 dog breeds are known to develop this disease as indicated in Table 1 (Zangerl et al., 2006; Andre et al., 2008).

Which breeds are affected by PRA-prcd?

 

Table 1: Dog breeds commonly affected by PRA-prcd

Popular South African breeds American Cocker Spaniel Australian Cattle Dog Australian Shepherd Chinese Crested Dog English Cocker Spaniel Golden Retriever Labrador Retriever Miniature Poodle Toy Poodle Yorkshire terrier

Less popular breeds American Eskimo dog Australian Stumpy Tail Cattle Dog Chesapeake Bay Retriever Cockapoo Entelbucher Mountain Dog Finnish Lapphund Kuvasz Labradoodle Lapponian Herder Nova Scotia Duck Tolling Retriever Portuguese Water dog Spanish Water Dog Swedish Lapphund

 

How is the disease inherited?

Each animal has two copies of each gene, one inherited from its mother and one from its father. PRA-prcd is an autosomal recessive disease that affects males and females equally.

 

An autosomal recessive disease implies that two copies of the disease mutation needs to be present in order for the animal to display disease symptoms. 

 

The causative mutation occurs in the PRCD gene on chromosome 9 and entails the substitution of a GTP with an ATP. This substitution of nucleic acids alters the amino acid composition of the protein and causes the disease.

 

Testing for PRA-prcd

There is no cure for PRA-prcd but the test offered by Inqaba biotec indicates if the dog is clear (homozygous for GTP), a carrier (heterozygous) or affected by the causative mutation (homozygous for ATP).

 

Clear: Both copies of the gene are normal (homozygous for ATP) therefore the dog will not display the disease symptoms, nor will it pass the mutant copy to its offspring.

 

Carrier: One copy of the gene is normal and one copy is a mutant copy (heterozygous). These animals will not display the disease symptoms, but may pass the mutant copy to its offspring.

 

Affected: Both copies of the gene are mutant (homozygous for ATP) and these dogs are very likely to display the disease symptoms. Affected dogs will pass the mutant copy to its offspring.

 

What are the breeding implications for my dog?

Table 2 gives a representation of the mating outcome of dogs with different PRA-prcd statuses. The percentage given is the probability for each pup to be clear, a carrier or affected by the causative mutation.

 

Table 2: Possible mating outcomes

Parent 1 genotype	Parent 2 genotype
	Clear	Carrier	Affected
Clear (No mutant   copies)	All Clear	50% Clear 50% Carrier	All Carrier
Carrier (One mutant copy)	50% Clear 50% Carrier	25% Affected 25% Clear 50% Carrier	50% Carrier 50% Affected
Affected (Two mutant copies)	All Carrier	50% Carrier 50% Affected	All Affected

   

Testing can be done at any age.