Dominant PRA in English Mastiffs and Bullmastiffs

The Progressive Retinal Atrophy, also known as "PRA" is a disease that causes degeneration of retina. The light-sensitive cells of the retina gradually die, because of insufficient blood vessels. The retina is formed by two types of photoreceptor cells: rods and cones. The rods distinguish between the shades of grey and are more sensitive to light and enable dim light vision. The cones are responsible for colour vision. The disease is inherited. It was described for the first time in 1911 in Gordon Setters and since that it has been recognised in most dog breeds, in wolfs and even in humans.

There are several forms of PRA. The PRA occurring in English mastiffs and Bullmastiffs differs from other types of canine retinal degeneration in particular by its significant dominant inheritance.

The dominant PRA is caused by mutation in rhodopsin (eye pigment) - a receptor connected with G-protein that is activated by light and initiates a cascade of reaction resulting in night vision. The mutations in RHO-gene have been first described in humans as a main cause of the dominantly inherited blindness connected with the retina degeneration (RP). In mastiffs and bullmastiffs, the point mutation p.Thr4Arg in RHO-gene (Kijas et al. 2002) has been identified as the cause of retinal degeneration (dominant PRA). It is a dominantly inherited degeneration of the retina resulting first in night blindness that can be identified in puppies at six weeks of age. The photoreceptors of the retina are gradually destructed, while the rods degenerate faster than the cones, and therefore, the night blindness occurs as the first sign. The night blindness progresses gradually in blindness and at the age of 1 to 2 years, most dogs affected with this disease are totally blind.

The AD-PRA is an autosomal dominant inherited disease - that means that only one copy of the mutated gene causes the disease occurrence in dogs. There are only healthy dogs or affected dogs; there are no carriers of this disease. In some dogs, a slower form of the retina degeneration may occur and the signs of the disease (night blindness) can be observed in adult age of a dog - with regard to the dominant inheritance of the disease, the health condition of a dog must be determined before the planned breeding and mating!

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References:

Kijas JW, Cideciyan AV, Aleman TS, Pianta MJ, Pearce-Kelling SE, Miller BJ, Jacobson SG, Aguirre GD, Acland GM..:Naturally occurring rhodopsin mutation in the dog causes retinal dysfunction and degeneration mimicking human dominant retinitis pigmentosa .Proc Natl Acad Sci U S A. 2002 Apr 30;99(9):6328-33. Epub 2002 Apr 23.