British researchers have theorized that a dominant gene causes glaucoma in the Welsh Springer Spaniel and the Great Dane, which have a high incidence in England but not in the United States, Dr. Gelatt said. But researchers only know the mode of inheritance in the Beagle. In Beagles, an autosomal (a chromosome other than a sex chromosome) recessive gene causes glaucoma, meaning males and the females are affected equally and unaffected dogs can be carriers.
Evidence collected by a Website survey set up by Dean Knudson, DVM, and veterinary ophthalmologist Dennis Olivero in Minneapolis, also points to a simple autosomal recessive pattern of inheritance in the Welsh Terrier. University of Missouri researchers are collecting DNA from Welsh Terriers in preparation for seeking a gene marker, a specific sequence of DNA that occurs only in dogs with glaucoma, and Dr. Gelatt's team is working on a DNA test for the Beagle.
Many people think in terms of breeding a heritable disease out of a canine population, but Dr. Gelatt hopes to take it further. "If we can find the 'nasty' gene, we may be able to find the 'normal' gene and inject that into the Beagle with the glaucoma gene before the glaucoma occurs," he said. Such a tactic would cure the disease one breed at a time, he said. "This is one long-term goal, and the Beagle, because we know so much about it, probably will lead the way."
While the future is hopeful, owners and veterinarians now face frustration. Dogs with primary glaucoma will slowly go blind, and while treatment may slow the disease, current treatment options don't cure it. The poor prognosis makes owners feel helpless. "It comes as a blow to people when they find out that the end result of primary glaucoma anyway is usually blindness," Dr. Knudson said. "In some cases, it can be managed well, but less than 10 percent of dogs with primary glaucoma that have medical treatment have vision at the end of the first year."
Knudson learned firsthand how the prognosis feels when his 5-year-old Welsh Terrier, Mac, was diagnosed with primary glaucoma and secondary lens luxation in both eyes in 1996. He and wife Joy Schlichting are veterinarians at Hillcrest Animal Hospital in Hudson, Wis. But their expertise and quick actionthey sought a specialist as soon as they noticed the signscouldn't save Mac's sight. He lost his vision over the next 18 months.
Orr had a similar experience with Patches. Symptoms first showed up about 18 months ago as a cloudiness in one eye. Assuming it was a cataract, Orr took him to a veterinarian. She's not sure what the veterinarian did for her dog and, feeling uninformed, sought treatment elsewhere when Patches' good eye began to cloud.
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