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Dogs and humans share gene mutations for eye disease retinitis pigmentosa


English mastiffs are the giants of the dog world. Some of these gentle giants suffer from an eye disease similar to the human disease retinitis pigmentosa, a hereditary disorder that causes progressive vision loss and blindness. In a new study, scientists have identified the same disease-causing mutations in certain groups of mastiffs and humans. Establishing the groups' similarities and relevance to one another should improve future research and treatment.

An English mastiff dog (without PRA).

Retinitis pigmentosa is a disease of the retina, caused by mutations in the rhodopsin gene. These mutations alter the rhodopsin proteins' ability to regenerate to their original shape in dim light, and thus the retina does not perceive light normally.

The gene defect for retinitis pigmentosa in humans was found in 1990, but until now, scientists have been unable to identify the same, naturally occurring gene mutations in other mammals.

Members of the Mastiff Club of America noticed the blinding and debilitating disease in their pets and brought it to the attention of the researchers at Cornell University's Baker Institute for Health in Ithaca, NY. Dog owners provided information about the pedigree and family histories of dogs so that the scientists could establish a mode of inheritance.

Composite image, made through an ophthalmic instrument, shows damage to the retina of an English mastiff with PRA.

"If they didn't bring the disease to our attention, it would have been difficult to find out," says James W. Kijas, who led the study at Cornell.

The scientists discovered that the disease in mastiffs is dominantly inherited, which means that the presence of a single abnormal gene from either parent causes the disease in offspring. This type of inheritance mimics a form of retinitis pigmentosa in humans. The researchers examined the gene mutation and found that the genes are located in the same region of the human and the dog genome.

Next, the researchers conducted clinical tests at the University of Pennsylvania's Scheie Eye Institute to examine the retinal function of affected dogs. They used electrical impulse tests to determine how the retina molecules respond to light and found that the same mechanical defects cause the eye disease in mastiffs and humans, confirming the similarities between both groups.

"This model should advance understanding of the pathophysiology of the disease and therapies for this major subset of dominant retinitis pigmentosa," the researchers write in Proceedings of the National Academy of Sciences.

The research has also contributed to the development of a new screening test to determine if a dog has the defective gene before even exhibiting symptoms of the disease. Pet owners and members of the mastiff club hope to eventually 'breed-out' the defective gene.

See related GNN article
»Mapping the Dog

Mastiff Club of America

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Kijas, J.W. et al. Naturally occurring rhodopsin mutation in the dog causes retinal dysfunction and degeneration mimicking human dominant retinitis pigmentosa. Proc Natl Acad Sci USA 99, 6328-6333 (April 30, 2002).

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