Genetic Test For PKD


Published Julne 2004

Great News!

Dr. Leslie Lyon announced in the University of California (Davis) newsletter, Center for Companion Animal Health, that an electrophoretic gel demonstrating heterozygosity at the PKD gene locus for a cat with PKD has been developed.

Researches at UC Davis continue working on refining the PKD DNA test. They hope up have it
commercially available by the summer of 2004.

"Now as soon as a kitten is born, we will be able to know with nearly 100 percent accuracy whether the animal carries PKD.

A Short History of PKD and the Cat Fancy

Feline Polycystic Disease (PKD) is an inherited kidney disease that has been found in some breeds of cats including Persians and Exotics.

Polycystic disease is a disease that shows up later in life (late onset) with enlarged kidneys and kidney dysfunction occurring between three and 10 years of age (on average at seven years of age). The condition is inherited and cysts are present from birth, but are smaller in younger animals. Cyst size can vary from less than 1 mm to greater than 1 cm in size, with older animals having larger and more numerous cysts. Problems occur when these cysts start to grow and progressively enlarge the kidney, reducing the kidney's ability to function properly. The ultimate end is kidney failure. Some of the clinical signs are depression, lack of or reduced appetite, excessive thirst, excessive urination and weight loss. There is a marked difference in when and how quickly individual cats succumb, with the possibility of this developing late enough in life that the cat can die of other causes before kidney failure. However, kidney failure is certain when the cysts can grow and cause problems. Rarely, cysts are also seen in other organs such as the liver and uterus.

Reported sporadically in veterinary literature since 1967, actual study into this renal disease did not begin until 1990. By the late 1990's, David S. Biller, DVM, DACVR and Stephen DiBartola, DVM, DACVIM conducted a study at Ohio State University that rocked the Persian cat breeding world.

Ultrasound

The test for PKD status became an ultrasound of the kidneys at 10-12 months of age. Initially, this was reported to be 98% accurate. Breeders organized day long PKD clinics where a sonographer would scan cat after cat, reducing the costs to about $35/cat from the usually ultrasound fees of $250.

False Negatives

As breeders began to sell kittens as "out of negative parents", there were cases of these kittens being scanned positive.

Initially, the false negative reading were usually blamed on inexperienced sonographers or poor scanning equipment.

But, the same thing happened to cats scanned by the top men in the field.

What many breeders (and perhaps sonographers) acknowledge was that 98% accurate (a prediction that was probably overly optimistic), actually meant that for every 50 cats scanned, one would be wrong. If you assume most cat breeders have between 10-15 cats, that means every 3 or 4 breeders who have scanned all their cats negative, statistically have an unknown positive...

Third Generation

And indeed, there have been repeated cases of cats sold as 3 generation negative, who were discovered to be positive. Re-scanning discovered a problem 3 generations back!

The call for a genetic test increased.

PKD Gene Identified!

The gene responsible for autosomal dominant PKD was found in December 2003. Researchers began intense study to develop a genetic test and have spent the last three months verifying the work in a variety of cats.

The Test

If folks want to use the precise brand that Leslie was passing out at the Genetics Conference last year, it was CytoSmear from PurFybr Inc., cat. no. 4653BS.

Actually even sterile cotton swabs will work, but cytology swabs tend to give more consistent adequate sample volume

Here is a link that gives a hint as to how sample collection and submission will be performed. I am guessing that the test will probably be approximately $40 per cat for PKD testing, but I don't
have that confirmed yet. http://www.vgl.ucdavis.edu/service/parentage/

The tissue brushes (also called cytology brushes) can be obtained from your veterinarian, or may be purchased by the box of 100 at medplususa.com

The sample required is identical. Both tests simply need enough nucleated cells to extract a sufficient quantity of DNA. The cervical brushes are a widely used tool for sample collection of this nature, both in human molecular biology and for veterinary DNA
testing.

The Future

The work has been submitted for publication in a scientific journal and for a patent.

Pricing and sample handling procedures are not yet available, but a simple genetic test for the PKD gene will hopefully be available by the summer of 2004.


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