Progressive Retinal Atrophy (Type A) - PRA-A

 

Overview

PRA is a progressive disorder of the retina (the innermost layer of the eye) that leads to blindness in dogs. Type A PRA is the progressive degeneration of the retinal tissue. Normally the vision receptors in the eyes undergo a continual process of replacement and renewal, with PRA this process slows and eventually stops.

The thinning of the retinal tissue leads to the degeneration of the photosensitive receptors sensitive to dim light (rods), causing night blindness, and then the receptors sensitive to bright light (cones), causing day blindness. Type A PRA it is usually not seen until 2-5 years of age.

Severity - 4

Type A PRA has a moderate-high degree of severity as it can occur as a partially dominant trait, carriers can show signs of the disease despite not being genetically ‘affected’.

Symptoms

PRA does not always have noticeable symptoms until it is in relatively advanced stages. Type A PRA is a difficult form of retinal atrophy as it can be partially dominant; some carrier animals appear partially affected when examined clinically. An abnormal shine may be apparent in the dog’s eyes as a result of increased pupil dilation, as the eye attempts to let in more light. The pupil will appear dark and glossy, and will not respond as quickly to light as an unaffected dog. Disorientation is also common symptom of PRA, particularly at night due to the degeneration of the light sensitive rods specializing in dim light perception. Initial night blindness in most cases will progress slowly to day blindness also as the cones in the eye that respond to bright light are progressively damaged. Sadly, like humans, there is no treatment or cure for blindness in dogs.

Genetic Testing

Animal Network provides a DNA test that determines the genetic predisposition to type A PRA.

Progressive Retinal Atrophy (type A PRA) is an autosomal recessive disease. A recessive phenotype (trait or disease) will only be expressed when two copies of the recessive gene variant are present; however Type A PRA can appear partially dominant in carriers. A direct gene test can detect whether a dog is clear, carrier or affected by the disease.

A carrier holds one copy of the disease-causing gene, however due to the partial dominance of the disease; a carrier may or may not exhibit symptoms of PRA. There is an increased chance of offspring being affected (partially or completely), than a usual autosomal recessive disease. Genetic testing is highly recommended due to the seriousness of the disease, even if no symptoms are present. It is advised that carriers and affected dogs be excluded from breeding programs.

For an explanation of possible genetic status of offspring please refer to our fact sheet on Breeding strategies. ORDER A TEST

Breeds Affected

Miniature Schnauzer


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