Renal Dysplasia In Shih Tzu

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, Lhasa Apsos, and Soft Coated Wheaten Terriers and is believed to be genetically identical in these three breeds; a similar, but not genetically identical disease 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.

First DNA Linked Marker Test for RD 

At this point, due in part to the aid of the Lhasa Apso breeders who initiated the research project and funding being provided by the ASTC for the salary and benefits of a full-time researcher at the University of Michigan, VetGen has come up with the first linked marker DNA test for the disease. This simple and noninvasive test, performed from a DNA sample collected on a cheek swab by the owner of the dog, can be performed even on puppies and will detect carriers as well as affected dogs. Although the test has its limitations, breeding only dogs that test clear will reduce your likelihood of producing puppies with renal dysplasia by about 80%. It is, therefore, much better than any other method we now have to begin eliminating the disease from our breed, and we strongly urge that all breeding stock be tested. To find out more about this test and how to obtain a cheek-swab kit to have your dog tested, please go here.

The information provided by samples submitted for this test will help with further research to locate the specific defective gene, to find out whether this gene is dominant or recessive, and to determine whether a second defective gene is also involved in the disease. The researchers are still seeking cheek swab samples from Shih Tzu known to be affected by renal dysplasia and dogs that have produced offspring known to be affected with the disease, plus samples from Shih Tzu over the age of 13 with normal urine specific gravity readings. The dogs do not have to be related, and their identity will remain strictly confidential.