Renal dysplasia is a developmental or genetic defect of the kidneys. This makes it quite different from common forms of kidney disease which occur in adult or aged dogs and from other diseases and/or drugs which may cause inflammation of the kidneys and abnormal results on blood and urine tests of kidney function. Dogs affected with renal dysplasia have had an embryonic arrest in kidney development at some time around birth. The immature nephrons normally found in young puppies persist throughout life. Also, some nephron units do not develop and are replaced with fibrous tissue. There may be diffuse interstitial fibrosis in the cortex and medula, reduced numbers of glomeruli, dilated and hypoplastic tubules, and a variety of sizes of glomeruli. The disease is found most commonly in Shih Tzu and Lhasa Apsos, although it is also present, with less frequency, in several other breeds.
The disease usually progresses in three stages, each of which may have a variable and independent time course. Stage one is the silent destruction and loss of nephrons over a period of months and years in the absence of symptoms. Stage two occurs when approximately 30% of functioning nephrons remain and clinical symptoms (excessive thirst and volume of urine, weight loss, lack of vigor, and intermittent loss of appetite) are first obvious. This stage may persist for months or years. In the final stage, vomiting, weakness, dehydration, and severe debilitation are added to second stage symptoms, and death from renal failure (uremia) is the eventual outcome.
One may become suspicious of renal dysplasia in puppies older than eight weeks if excessive thirst, excessive volumes of urine, and pale urine are noticeable. Normal Shih Tzu puppies drink approximately one ounce of water per pound of body weight daily when eight to ten weeks of age, but dogs with severe renal dysplasia may drink as much as five times that quantity. Such puppies may also demonstrate reduced body weight and stature compared to normal puppies. They commonly weigh less than three pounds at five months of age and progress to renal failure quickly. Moderately affected puppies may appear normal until five or six months of age and then follow the same course, with chronic debilitation and death at nine to twelve months. Many animals with the disease, however, are only slightly affected and will live a normal life with normal renal function. Nevertheless, they can pass on some degree of the defect to their offspring.
BUN and creatinine, the two common blood tests of renal function, are not elevated until 70 to 75% of the kidney is nonfunctioning, and therefore are of little use in identifying mildly or moderately affected dogs. Having a BUN and creatinine in the normal range means that the dog has at least 30% kidney function. It does not mean that the dog is free of renal dysplasia. Elevated BUN and creatinine readings may also be caused by other renal problems, but these tests can be of some use in identifying severely affected dogs, particularly puppies already drinking and urinating excessively. Most adult Shih Tzu with normal kidneys also have a urine specific gravity reading above 1.045. This is another test of kidney function; it does not tell you that your dog is free of renal dysplasia. Ultrasound examination of the kidneys may be slightly more useful in identifying moderately affected dogs, whose kidneys may be smaller than normal size and show scarring. Only a wide wedge biopsy of the kidney can currently provide a definitive diagnosis of renal dysplasia and identify slightly affected dogs by showing the fetal glomeruli that provide definitive proof of renal dysplasia. (A needle biopsy does not supply enough tissue for diagnosis and is of no value.)
This disease at the present time presents a real dilemma for breeders. It may go undetected for many generations or be ignored by knowledgeable breeders because it is transmitted in a very silent fashion by many animals that appear clinically normal, and because many breeders are unwilling to subject their dogs to the surgery that is now the only definitive way to identify the presence of the disease.
The American Shih Tzu Club is actively involved in a research project to find a genetic marker for renal dysplasia, which is being done by VetGen in Michigan. Locating such a genetic marker will mean that we will ultimately be able to determine whether an animal has any degree of renal dysplasia through a simple and noninvasive test done on a cheek swab. Even puppies could be tested at a relatively young age. Once the marker is located, VetGen will be able to perform the cheek swab test on any Shih Tzu for about $120, with discounts for a large number of dogs tested at one time. Hopefully, such a test will ultimately eliminate the disease from our own and other breeds.
At this point, due to the aid of the Lhasa Apso breeders who initiated the research project, VetGen researchers have narrowed the search to only three genes and expect to locate such a marker within two years. They are now also working with Shih Tzu. To locate the specific marker, they are seeking cheek swab samples from Shih Tzu known to be affected by renal dysplasia through wide wedge biopsies and dogs that have produced offspring known to be affected through the results of such biopsies. The dogs do not have to be related, and their identity will remain strictly confidential. Please, if you own or know of such a dog or dogs, contact Joann Gustafson of the ASTC Renal Dysplasia Committee at 1829 F & S Grade Road, Sedro Wooley, WA 98284-9664. She will send you cheek swabs (you can take the samples yourself) and instructions for sending the samples to VetGen. Also, ask your veterinarian if he knows of any such dogs and is willing to contact their owners with this information. The sooner we collect the needed samples, the sooner the test will be available. If you can, for the sake of the breed we all love, please do your part to help us eliminate this disease.