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Concept
Progressive retinal atrophy
Résumé
Progressive retinal atrophy (PRA) is a group of genetic diseases seen in certain breeds of dogs and, more rarely, cats. Similar to retinitis pigmentosa in humans, it is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an autosomal recessive trait, with the exception of the Siberian Husky (inherited as an X chromosome linked trait) and the Bullmastiff (inherited as an autosomal dominant trait). There is no treatment.
In general, PRAs are characterised by initial loss of rod photoreceptor cell function followed by that of the cones and for this reason night blindness is the first significant clinical sign for most dogs affected with PRA. As other retinal disorders, PRA can be divided into either dysplastic disease, where the cells develop abnormally, and degenerative, where the cells develop normally but then degenerate during the dog's lifetime.
Generalized PRA is the most common type and causes atrophy of all the neural retinal structures. Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED).
Commonly affected breeds:
Akita - Symptoms at one to three years old and blindness at three to five years old. Selective breeding has greatly reduced the incidence of this disease in this breed.
Miniature longhaired Dachshund - Symptoms at six months old.
Papillon - Slowly progressive with blindness at seven to eight years old.
Tibetan Spaniel - Symptoms at three to five years old.
Tibetan Terrier - PRA3/RCD4 disease of middle age dogs.
Samoyed - Symptoms by three to five years old.
This type of PRA has an early onset of severe vision loss. It is caused by a defect in the gene for cGMP-phosphodiesterase, which leads to retinal levels of cyclic guanosine monophosphate ten times normal.
Irish Setter - Rod cell response is nearly absent. Night blindness by six to eight weeks old, often blind by one year old.
Source officielle
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