PON-Pedigrees

The Disease

Progressive retinal atrophy (PRA) is a major hereditary cause of blindness in pedigree dogs as is its counterpart retinitis pigmentosa (RP) in humans. PRA shows genetic heterogeneity, as does RP, with several distinct forms already recognized and several more remaining to be investigated.

One can distinguish between late onset forms of PRA and early onset (whelp-age) dysplastic changes. The clinical and ophthalmologic signs of both forms are similar. Affected dogs suffer from bilateral Mydriasis, the reflection of the Tapetum lucidum is increased and the retinal vascular network appears atrophic.

The rcd4 PRA is another form of PRA, it is also known as LOPRA (Late Onset PRA) the age of onset of dogs with LOPRA varies from few years of age (2-3 years) up to old age (10-11 years)

Rcd4

Clear

Genotype: N / N [ Homozygous normal ]

The dog is noncarrier of the mutant gene.
It is very unlikely that the dog will develop Progressive retinal atrophy ( rcd4-PRA) / LOPRA. The dog will never pass the mutation to its offspring, and therefore it can be bred to any other dog.

Carrier

Genotype: N / rcd4 [ Heterozygous ]

The dog carries one copy of the mutant gene and one copy of the normal gene.
It is very unlikely that the dog will develop Progressive retinal atrophy ( rcd4-PRA) / LOPRA but since it carries the mutant gene, it can pass it on to its offspring with the probability of 50%.

Carriers should only be bred to clear dogs.

Avoid breeding carrier to carrier because 25% of their offspring is expected to be affected (see table above)

Affected

Genotype: rcd4 / rcd4 [ Homozygous mutant ]

The dog carries two copies of the mutant gene and therefore it will pass the mutant gene to its entire offspring.
The dog is likely to develop Progressive retinal atrophy ( rcd4-PRA) / LOPRA and will pass the mutant gene to its entire offspring