Progressive Retinal Atrophy (X-Linked) - XL-PRA
OverviewPRA is a progressive disorder of the retina (the innermost layer of the eye) that causes blindness in dogs. 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. Areas of the retina that express the defective X chromosome deteriorate and this leads to the progressive degeneration of the surrounding retina. XL-PRA affected dogs, suffer from different mutations of the same gene, and the severity of the disease differs between the two affected breeds. This form of PRA has a late onset; first signs are usually not seen until around 3-5 years, though deterioration can begin as early as 5 months of age.
Severity - 4
XL-PRA has a moderate-high degree of severity due to the mode of inheritance, as it is X-linked; there is a much higher risk of affected offspring from carriers, particularly males.
XL-PRA affected dogs usually have a characteristic shine to their eyes as their pupils become increasingly dilated in the attempt to let in more light. Affected dogs will often develop ‘tunnel vision’ as their retinal tissue deteriorates. Disorientation is also common, particularly in dim light in the early stages of degeneration, before progressing to complete night blindness and eventually day blindness. Female carriers often show signs of partial retinal defects, though it does not usually affect their vision. It is important that females in particular are tested before breeding in order to control the disease, as sadly there is no treatment or cure for blindness in dogs.
Animal Network provides a DNA test that determines the genetic predisposition to X-Linked PRA.
Progressive Retinal Atrophy (XL-PRA) is a sex linked recessive disorder in which the recessive trait is situated on the X chromosome. A direct gene test can detect whether a dog is clear or affected by the disease. Females who inherit a single affected X chromosome are carriers and will show partial retinal degeneration, while those with two affected X chromosomes are affected by the disease. Males have one X chromosome and only require a single affected X in order to be affected. It is highly recommended that dogs are tested before breeding, and that female carriers are excluded from breeding programs in order to reduce the risk of affected male offspring.
For an explanation of possible genetic status of offspring please refer to our fact sheet on Breeding strategies. ORDER A TEST