RCD4

Progressive retinal atrophy

Name: Progressive Retinal Atrophy (rcd4-PRA)
Gene Location: PCARE
Chromosome: 17
Mutation: c.3149_3150insC
Symptom Complex: Ophthalmic
Inheritance: Autosomal recessive
Test type: Direct mutation test
Typical onset age: ~10 years

Note: these information are only valid for Tibetan Terriers.




General Information

The Progressive Retinal Atrophy (PRA) leads to a degeneration of the retina and results in blindness. The Rod-cone-dysplasia type 4 (rcd4)-PRA is characterised as a Late Onset PRA (LOPRA). Night blindness is a typical first symptom of the disease. However, not all ophthalmological PRA-affected Tibetan Terriers could be explained by RCD4. 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 10 years of age, though it can occur between 5 and 12 years.
  • Night Blindness (Nyctalopia):
    This is usually the first noticeable symptom, where the dog has difficulty navigating in low light or at dusk.
  • Clumsiness and Hesitance:
    Affected dogs may become hesitant to enter dark or unfamiliar rooms and show reduced confidence at night.
  • Vascular Attenuation:
    The retinal vascular network appears narrowed or "atrophic" in later stages due to reduced blood flow needs of the dying retina.
  • Pupillary Changes:
    Affected dogs often show dilated pupils (mydriasis) and slow or incomplete pupillary light reflexes (PLR).
  • Progressive Loss of Daylight Vision:
    While starting as night blindness, the condition eventually progresses to affect daytime vision and leads to complete blindness.
  • 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.
While the average age of diagnosis for RCD4 is 10, clinical signs can begin manifesting between 5 and 12 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 Pet Pursuit 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/RCD4 Pet Pursuit CARRIER / N/RCD4 = Dogs with N/RCD4 genotype are generally clinically healthy and do not develop the disease. If N/RCD4 dog is affected by PRA, it’s different PRA-gene or unknown mutation.
AFFECTED / RCD4/RCD4 Pet Pursuit AFFECTED / RCD4/RCD4 = Dogs with RCD4/RCD4 dogs appear normal at birth, but begin to exhibit clinical effects later. Symptoms often appear between around 5-12 years of age. The age of onset of the disease can vary greatly among individuals.
PRA
PRA



Inheritance
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