Late-Onset PRA Diagnoses in Tibetan TerriersProbably CCL, A Different Genetic ConditionDNA Bank & Registry Requesting Blood SamplesTo Develop Genetic Tests for These Eye Conditions A review of CERF statistics for Tibetan Terriers has shown two separate peaks in the incidence of retinal problems. The first peak occurs at about 2 to 3 years of age, and the second peak starts at about 5 to 7 years. Some ophthalmologists and Tibetan Terrier owners previously characterized all of these changes as progressive retinal atrophy, PRA. However, recent studies of some of these dogs have indicated that the late onset retinal changes are probably due to canine ceroid lipofuscinosis, CCL, an entirely different genetic condition. In CCL, lipofuscin particles or "inclusions" build up in the tissues, and the brain may actually shrink in size. In the eye, the disease is characterized by inclusions in the retina. These retinal incusions build up with age in the inner nuclear and ganglion layers. They are most prevalent by 3 years of age and are autfluorescent on histological examination. The veterinary ophthalmologist will start to observe ophthalmoscopic changes at 3 or 4 years of age. The first signs of CCL in the Tibetan Terrier may be nyctalopia, or night blindness, which may occur as early as 7 weeks and will show up on an electroretinogram (ERG). This test detects electrical signals given off by the cells of the retina when they respond to light. Initially, the ERG displays what ophthalmologists refer to as a characteristic negative b-wave amplitude. One of the early signs of CCL is an almost complete loss of the b-wave. As time progresses, and as the slow degeneration process continues, the ERG changes to an extinguished pattern. Nyctalopia may be the only functionality abnormality for several years. Then, starting at 4 to 6 years, personality and learning changes, along with mild functional abnormalities, will gradually show up. These signs include: loss of house training; confusion; or dementia-like behavior; easily frightened; occasional, unpredictable aggressiveness; and appetite changes (from poor to ravenous). Ataxia (problems with muscle coordination) may develop. Day vision may remain until about 9 years of age. Request for Blood Samples The Tibetan Terrier DNA Bank & Registry is a project funded under a grant from the Canine Health Foundation and the Orthopedic Foundation for animals (CHF Active Grant # 1652). DNA and morphology profiles are being collected to create a multi-genertional repository. Its purpose is to: (1) provide samples for genetic research without the need to raise and breed study samples; (2) provide the information needed to help reduce the incidence of the genetic problems in this breed; and (3) act as a pilot project for development of similar registries in other breeds. Genetic problems in Tibetan Terriers include several affecting the eyes: PRA, lens luxation, cataracts, and ceroid lipofuscinosis. The project is interested in participation of as many Tibetan Terrier owners as possible, with the intent of obtaining a large enough sampling of both affected and normal dogs to be able to perform genetic marker studies. Gary S. Johnson, DVM, Ph.D., Associate Professor of Pathobiology at the University of Missouri-Columbia, is Principal Investigator. Any help Tibetan Terrier owners can provide by participating in the project will also be greatly appreciated. Any help ophthalmologists can provide in referring Tibetan Terriers owners to the project will also be appreciated. Possible Diagnosis, Treatment for CCL The owners of those dogs suspected to have CCL who participate in the projects may also be able to take advantage of other diagnostic tests and experimental treatment regiments. Martin L. Katz, Ph.D., Associate Professor at the University of Missouri-Columbia, who has completed studies on CCL in the English Setter, will be studying this disease in the disease in Tibetan Terriers. Dr. Katz is looking at the possible biochemical basis of CCL. He is evaluating the correlation between blood carnitine levels and the incidence of CCL, and in suspected cases he is confirming the presence of cellular inclusions through electron microscopy. Possible experimental treatment protocols may include: dietary supplementation to delay the onset of symptoms of the disease; and drug therapy to prolong the functionality of affected neurons. It still remains to be shown that the biochemical basis of the disease is the same in Tibetan Terriers as it is in English Setters, and it is important to understand this to avoid the potential of building any false hopes or expectations. However, if you have a Tibetan Terrier which you believe may have CCL, your participation would be extremely helpful in the development of potential diagnostic tools and treatment regiments for this condition. The Tibetan Terrier DNA Bank & Registry has developed blood collection kits which include all the supplies for the veterinarian and forms for the dog owner. Fedex shipping is covered by the CHF grant. Please let us know if you would like any kits, either for your own use or to provide to your patients. Tibetan Terrier pet owners and breeders: The Tibetan Terrier Club of America has additional information that may be helpful in the diagnosis and treatment of dogs with CCL. To request that information, contact Stuart Eckmann or Linda Bell at the e-mail address below. Ophthalmologists, neurologists, and other veterinarians: The Tibetan Terrier Club of America has published an article, Major Inherited Eye Problems in Tibetan Terriers, by Lionel F. Ruben, VMD, which may be helpful in the differential diagnosis of CCL and PRA. To request a reprint of the article, contact either Stuart Eckmann or Linda Bell at the e-mail addresses below. For collection kits, more information about or to refer patients to the Tibetan Terrier DNA Bank & Registry, contact: Liz Hansen
For more information about, or to refer Tibetan Terriers for, CCL and carnitine evaluation, contact: Stuart F. Eckmann
Linda W. Bell
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