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PRA3

Progressive retinal atrophy

Name:	Progressive retinal atrophy (PRA3)
Gene Location:	FAM161A
Chromosome:	10
Mutation:	c.1758-15_1758-16ins238
Symptom Complex:	Ophthalmic
Inheritance:	Autosomal recessive
Test type:	Direct mutation test
Typical onset age:	~5 years~

Note: these information are only valid for Tibetan Terriers.

General Information
Canine progressive retinal atrophies (PRA) are genetically heterogeneous diseases characterized by retinal degeneration and subsequent blindness. While there are PRA mutations that are shared by multiple breeds, many seem to be private to a single breed or are found in breeds sharing similar ancestral backgrounds. Typical signs found by ophthalmoscopic examination are widespread tapetal hyper-reflectivity and retinal vascular attenuation. Genetic testing complements clinical eye examinations with the advantage of detecting known PRA mutations before breeding age or before clinical signs present. In Tibetan Terrier, a genetic variant of the FAM161A gene has been found to cause a PRA form which is called PRA3. The FAM161A gene encodes for a ciliary protein expressed at the photoreceptors of the retina. However, not all ophthalmological PRA-affected Tibetan Terriers could be explained by PRA3. Therefore, additional unknown PRA causing variants are suspected besides to the PRA3 & rcd4-PRA variants in Tibetan Terriers.

General Information

Canine progressive retinal atrophies (PRA) are genetically heterogeneous diseases characterized by retinal degeneration and subsequent blindness. While there are PRA mutations that are shared by multiple breeds, many seem to be private to a single breed or are found in breeds sharing similar ancestral backgrounds. Typical signs found by ophthalmoscopic examination are widespread tapetal hyper-reflectivity and retinal vascular attenuation. Genetic testing complements clinical eye examinations with the advantage of detecting known PRA mutations before breeding age or before clinical signs present. In Tibetan Terrier, a genetic variant of the FAM161A gene has been found to cause a PRA form which is called PRA3. The FAM161A gene encodes for a ciliary protein expressed at the photoreceptors of the retina. However, not all ophthalmological PRA-affected Tibetan Terriers could be explained by PRA3. Therefore, additional unknown PRA causing variants are suspected besides to the PRA3 & rcd4-PRA variants in Tibetan Terriers.

Clinical features
Late-Onset Vision Loss: Symptoms typically begin around 5–7 years of age, though it can occur between 2 and 11 years. Initial Night Blindness (Nyctalopia): The first sign is often difficulty seeing in low light or dim settings, with dogs becoming more cautious at night. Progressive Daytime Blindness: Over time, the disease progresses to affect day vision, leading to complete blindness. Pupillary Changes: Affected dogs often show dilated pupils (mydriasis) and slow or incomplete pupillary light reflexes (PLR). Retinal Degeneration Features: Ophthalmoscopic examination typically reveals increased reflectivity of the tapetum (bright eye-shine) and attenuation (thinning) of the retinal blood vessels. Secondary cataracts As a common consequence of chronic retinal degeneration (PRA), affected dogs may develop secondary cataracts (clouding of the eye lens), which can further impair vision. Slow Progression: The disease is characterized by a slow, progressive degeneration of the rods and cones. Affected dogs show the typical symptoms of PRA3 at a relatively late age of onset, approximately most commonly at 5 years of age. While there is no cure, the disease itself is painless but secondary diseases could be painful. Please note that symptoms and age-frames may also be of other types and may differ from those mentioned above.

Clinical features

Late-Onset Vision Loss:
Symptoms typically begin around 5–7 years of age, though it can occur between 2 and 11 years.
Initial Night Blindness (Nyctalopia):
The first sign is often difficulty seeing in low light or dim settings, with dogs becoming more cautious at night.
Progressive Daytime Blindness:
Over time, the disease progresses to affect day vision, leading to complete blindness.
Pupillary Changes:
Affected dogs often show dilated pupils (mydriasis) and slow or incomplete pupillary light reflexes (PLR).
Retinal Degeneration Features:
Ophthalmoscopic examination typically reveals increased reflectivity of the tapetum (bright eye-shine) and attenuation (thinning) of the retinal blood vessels.
Secondary cataracts
As a common consequence of chronic retinal degeneration (PRA), affected dogs may develop secondary cataracts (clouding of the eye lens), which can further impair vision.
Slow Progression:
The disease is characterized by a slow, progressive degeneration of the rods and cones.

Affected dogs show the typical symptoms of PRA3 at a relatively late age of onset, approximately most commonly at 5 years of age. While there is no cure, the disease itself is painless but secondary diseases could be painful.

Please note that symptoms and age-frames may also be of other types and may differ from those mentioned above.

Morbidity
CLEAR / N/N		CLEAR / N/N = Dogs with N/N genotype will not have this variant of PRA. If N/N dog is affected by PRA, it’s different PRA-gene or unknown mutation.
CARRIER / N/PRA3		CARRIER / N/PRA3 = Dogs with N/PRA3 genotype are generally clinically healthy and do not develop the disease. If N/PRA3 dog is affected by PRA, it’s different PRA-gene or unknown mutation.
AFFECTED / PRA3/PRA3		AFFECTED / PRA3/PRA3 = Dogs with PRA3/PRA3 dogs appear normal at birth, but begin to exhibit clinical effects later. Symptoms often appear between 2-11 years of age. The age of onset of the disease can vary greatly among individuals.

Inheritance

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