RENAL DYSPLASIA

by Lisbeth Plant

 

Terms used in this article:

“Renal” = relating to the kidney; “Dysplasia” = abnormality in maturation; “Nephrons” = the smallest functioning units of the kidneys; “Nephropathy” = damage or disease of the nephrons; “Nephritis” = inflammation of the nephrons; “Glomeruli” = the small blood vessels of the kidneys.

 

Introduction

Renal Dysplasia (RD) is a very serious developmental disorder affecting the kidneys of puppies and young dogs. It is also known as Juvenile Renal Dysplasia (JRD) or (Juvenile) Progressive Nephropathy (PNP).

 

RD has gained increased attention in the Swedish berner community during the last 10 years. It was first diagnosed in a BMD in 1990. There is no cure; the dog dies or has to be euthanized because of kidney failure.

The BMD is only one of several breeds affected. Research to find a
genetic test for RD in Boxer is going on through a collaboration between the Broad Institute in Cambridge, MA, and the Swedish University of Agricultural Sciences.

Symptoms & Diagnosis

 

Affected puppies are born with underdeveloped kidneys, in which the nephrons are at a more juvenile stage compared to the development of the individual. The nephrons never reach maturity, so the kidneys never reach full capacity. Among the known Swedish cases, the average age at presentation is 15 months, but puppies may show symptoms even while they are still with the breeder.

 

Symptoms may vary between individuals and depend on the progression and severity of each case. They are similar to those involved in general kidney disease and include excessive drinking (polydipsia) and excessive urination (polyuria). Some puppies may seem difficult to housebreak, while others are fine until they start drinking a lot. They may develop a lack of appetite, weight loss, vomiting and/or dehydration. There may be pallor of the mucous membranes, a foul odour and uremic ulceration. Severely affected puppies will fail to thrive.

 

Depending on how far the disease has progressed, the urine sample will be dilute and with little colour and odour and will likely have protein in it. The blood test may show anaemia and increased BUN. On ultrasound examination, the kidneys will likely look small and irregular in shape. Post mortem, they are pale and tough, and sometimes nodular and distorted. Firm diagnosis can only be made with a kidney biopsy, or at a post mortem examination.

 

Mode of Inheritance

RD is believed to be caused by a simple autosomal recessive gene, i.e. both parents have to be carriers for a puppy to become sick. Statistically, 25% of the puppies from such a combination should become ill, 50% should be carriers, and 25% should be neither carriers nor affected. Unfortunately, Mother Nature is not that predictable and sometimes, many pups can become ill, and at other times, perhaps none at all. In addition, mildly affected dogs might die from other causes, like cancer, before they are diagnosed with RD, or very severe cases die as neonates and are never investigated by the breeder. Then there is no way of knowing that the parents actually carry this fatal disease or that their puppies may be carriers who will continue to pass the disease on. This is how disease genes can spread ‘quietly’ through a population before anybody realizes that there is a problem.

Kidney Disease in the Swedish BMD Population

The general occurrence of kidney disease in the Swedish berner population is estimated through pet insurance statistics to be around 0.33% per year (~5 dogs/year) while the estimated occurrence of RD is 0.08% (~1.3 dogs/year). The majority of kidney disease cases are therefore not RD. Since 1991, 21 cases of RD have been firmly diagnosed; 8 males and 13 females. Not all owners will agree to a kidney biopsy or a post mortem examination, so the real number is likely to be higher.

 

A less rare genetic kidney disease in BMD is Membraneous Glomerulonephritis (MGN), a.k.a. Familial Nephropathy (FN), which is believed to be inherited through a simple recessive gene. In the English Cocker Spaniel, MGN can be established through a genetic test, but there is not yet a test for BMD.

Even though it is not the most common of the inheritable kidney diseases, the Swedish breed club estimates that between 2 and 10 percent of the population are carriers of RD. As there is not yet any reliable genetic test to identify carriers, registration of known cases is necessary in order to control the spread of the disease.

 

Central Registration


When a cluster of RD cases occurred in the middle of the last decade, the Swedish breeder community was worried and caused the national breed club to apply to the Swedish Kennel Club (SKK) for the disease to gain Central Registration status. This was granted in 1998. "Central Registration" means that all veterinary clinics are informed about the disease and when a case is diagnosed, it will be reported to the SKK, who will register it in the open database (SKK HUNDDATA). Hip and elbow dysplasia are the other two genetic diseases that are subject to central registration for BMD at this time.


Control Programme

 

In addition to registration, parents and siblings of diagnosed dogs are excluded from the breeding pool. Half-siblings may not be bred before 2 years of age.

 

Because the risk of recessive disease genes manifesting themselves (=sick pups being born) is higher when the inbreeding coefficient is higher, breeders are encouraged to make sure to keep the inbreeding coefficient as low as possible, preferably between 2 and 2.5 percent.

 

The Swedish breed club maintains a list of the breedings that have produced known puppies with RD, as well as a list of affected puppies. The lists are available on the club’s website, so that all breeders can avoid using known carriers. They are also registered in Berner-Garde (www.bernergarde.org).

Go to: http://www.sshk.a.se/index.htm and click on “Renal Dysplasi (PNP)” in the left hand menu (halfway down under the second heading “Avelsrådet”. Scroll halfway down the page and there you find the two tables. The first one shows the list of litters with affected dogs, and their parents. The second table is the list of the 21 dogs that have a firm diagnosis. 13 of these 21 dogs were puppies between 2 months and 1 year old when diagnosed; five dogs were between 1 and 2 years old; two dogs were between 2.5 and 3 years old; and one was almost 5 years old.

 

The club will follow up the effectiveness of this control programme through the provisions of its Breeding Strategy Programme (“RAS”), which is being adopted this year.

 

***

Sources:

-          Svenska Sennenhundklubben (The Swedish Mountain Dog Club) - www.sshk.a.se

-          ”Textbook of Veterinary Internal Medicine” 6th Ed., 2005, by S J Ettinger, E C Feldman

-          “Clinicopathologic Principles for Veterinary Medicine” 1988 by W F Robinson, C R R Huxtable

-          The Broad Institute - www.broad.mit.edu

-          The Swedish University of Agricultural Sciences - www.slu.se