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Mastiff models eye ailment
The huge but gentle english mastiff, which sometimes carries the defective gene for the canine eye disease progressive retinal atrophy (PRA), has been shown to be a key animal model for retinitis pigmentosa (RP) in humans. The dogs, which can weigh on the order of 200 lb, can be used to test therapies for the human ailment, according to a team of scientists. RP currently causes vision loss and blindness in at least 100,000 people in the U.S. Team found the genetic mutation that leads to PRA blindness in the dog. Most recently, the group reported that "naturally occurring rhodopsin mutation in the dog causes retinal dysfunction and degeneration mimicking human dominant retinitis pigmentosa" The gene defect leading to RP in humans was found in 1990 and could be simulated by genetic manipulation in rats, mice, fruit flies, and pigs. Still, scientists wanted a large animal in which the inherited disease occurs naturally. One result of the current finding is a genetic screening test to help dog breeders eliminate the defective RHO gene from their lines of the purebred dogs. Team scientists, meanwhile, are studying dogs with the defective gene in the hope of answering a key question for both dogs and humans: What nongenetic or environmental factors cause the blinding disease to progress slowly in some individuals, more rapidly in others, and not at all in the few who seem to have the genetic mutation but don't go blind? The results might help to design treatments to halt, reverse, or even prevent some RP blindness in humans--experimental therapies that can now be tested first in dogs.
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