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Feline Health |
Polycystic Kidney Disease SeminarUpdate by Betty White Philadelphia, PA June 1998 The PKD Seminar was held in Philadelphia at the CFA Annual on Saturday at 2 pm and lasted, with questions and answers, until 4 pm. The group attending numbered about 75, a very good turnout considering the variety of options available that afternoon. Pamphlets which were reproductions of the CFA Health Committee website article on PKD were available. Joining me on the panel were Debi Faryna (NIH and one of our genetics advisors to Breeds and Standards), Sue Helmke (Marhei Persians), Hilary Helmrich (President of the Winn Foundation/Abydos Abyssinians and Persians), Dr. Leslie Lyons (NIH and presently involved in the Havana Brown project), and Anna Sadler (CFA Legislative Committee/Brannaway Persians). Following my introduction of the panel, I gave a short account of the beginning and development of the current interest in Polycystic Kidney Disease. [For informational purposes here, the first cases of PKD in cats were reported in the literature during the 1960s, and families of cats with PKD were identified in the 1970s. This was the first indication that PKD in cats is a heritable disease. However, it was not until the early 1990s that Drs. Biller, DiBartola, et al, actually characterized PKD in cats and showed that the disease mimics ADPKD in humans.] Sue Helmke then relayed the recommendations of the PKD Subcommittee. Sue's comments are quoted below: The PKD Subcommittee met Thursday afternoon with Dr. Biller. We have these suggestions for the breeders of Persians and related breeds: Sue went on to relate some of her own experiences with the disease and emphasized that pedigree research will not indicate "lines" affected due to the inability to test some of the "base" cats. The important thing is the here and now. She further reminded us that PKD positive cats are asymptomatic and may live a full life. Their offspring may or may not be severely affected and perhaps may eventually die of something unrelated to PKD. As Sue said, however, the end stages of renal failure are grim and should give one pause about avoiding the hard decisions associated with PKD. [Note: Many cats die of renal failure not associated with PKD because the kidney is a stressed organ in the cat. We can't change this; but cats with PKD can live a normal life.] The committee further suggests that an informative pamphlet about PKD be included in Persian (and related breeds) litter registrations. Hilary Helmrich spoke about the Abyssinian experience with renal amyloidosis, outlining the various responses Aby breeders made to the initial discovery of the disease. She said that the accusatory and denial phase seemed to last for about six months before breeders settled down to face the disease squarely and deal with it. A calm determination seems to characterize most Aby breeders today, and Hilary pointed out to the audience that RA is not nearly as easy to identify and eliminate as PKD. She further addressed the care of cats experiencing renal function deterioration. Anna gave us the history of the Dallas PKD clinic that really got the ball rolling as far as interest in this disease is concerned. She told the participants about how the sudden death of a four-year-old female, which necropsy confirmed was from PKD, led her to search for a way by which she could have all of her cats scanned. With this confirmed case of a disease that she knew to be heritable, Anna decided to "deal from knowledge rather than ignorance," as she always has. She knew she must screen all of her cats. This determination blossomed into the first-ever PKD screening clinic held in Arlington, Texas on May 2. Increasing interest, particularly after the Almanac article [February 1998], resulted in the registration of nearly 150 cats for this clinic. A human high-risk OB-GYN sonographer and Persian breeder, Pam Piveral, and the veterinarian for many of the breeders in North Texas, Dr. Kent Cooper, decided to participate. Dr. David Biller flew from Kansas to be with them as well. What everyone was unprepared for was to find that nearly 40% of the cats, from widely diverse lines and colors, tested positive. This was the electrifying news that galvanized breeders to set up similar clinics around the country. As of shortly before the annual, Anna reported that Barb Brush's Internet website, which is displaying all reported clinics and screenings, had results from more than 1100 Persians and cats of other breeds from the United States and other countries. [The figure as of July 13, 1998 is 2822.] Most clinics being set up with the recommended criteria are charging from $25-$50 per cat. The equipment itself is quite portable, making clinics possible in private veterinary offices, homes, hotel rooms, or even enclosed rooms at shows. Anna stressed that this screening is a very powerful tool to be used in making breeding and health management decisions. She said that the decision of whether to breed or immediately alter positive cats must be done on an individual breeder basis, and on a cat by cat basis. Knowledge of the cat's positive status can be invaluable in determining what antibiotics, anesthesias, etc., to be used will have the least negative impact on the kidneys. Debi Faryna had come prepared with all the latest published research relative to kidney disease, specifically cysts, should any challenge develop to either the nature of this disease or the validity of ultrasound testing for it. This did not occur; however, Debi has since provided some highly instructive information about this disease in human beings which should be stated. Polycystic Kidney Disease affects 600,000 Americans and more than 12 million people worldwide. Humans with PKD typically develop large cystic kidneys, and the majority develop kidney failure at some point in their lives. Other complications include brain aneurysms, enlarged heart, mitral valve prolapse in the heart, diverticulitis in the colon, chronic back or flank pain, groin or abdominal hernias, and pancreatic and liver cysts. It is highly variable and inheritable. Two forms have been identified in humans: Autosomal Dominant PKD (ADPKD), which primarily affects adults, and a much rarer form, Autosomal Recessive PKD (ARPKD), which affects children. Clinical diagnosis is generally made using ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI). Scientists are working on developing a DNA test to screen for ADPKD in humans. Debi Faryna answered questions with regards to the so-called "two hit" nature of PKD in human beings. In human ADPKD, scientists have found two genes that, when defective, appear to be responsible for ADPKD. These genes are referred to as PKD1 and PKD2. Defects in PKD1 have been shown to be affiliated with the greatest number of cases. A third gene has been shown to be defective in a very small number of ADPKD families; however, it has not yet been identified. Scientists have shown that cysts develop when both PKD1 genes are defective. It is proposed that people affected with ADPKD are born with one functional and one defective PKD1 gene. This is what scientists call the "first hit." Sometime during a person's lifetime, the sole functioning PKD1 gene is damaged in some cells, the gene is no longer able to replicate a specific protein, and cysts develop. This is referred to as the "second hit." This may account for the variability of the disease. Recently, investigators have found that PKD1 and PKD2 genes interact and suggest that this may explain why defects in either gene in human beings causes the same clinical disease. It should be pointed out that in both human beings and cats not all cysts of the kidney are inheritable diseases; there are other causes. Acquired cysts in cats are not inherited and are usually seen on only one kidney. However, PKD is unique in that it causes cyst formation bilaterally (on both kidneys). In addition, cyst formation will be shown to exist in either one or both parents. Scientists are working with Drs. Biller and DiBartola to find the gene(s) that causes ADPKD in cats. Once the gene(s) are identified, a DNA test can be developed to screen for ADPKD in cats. Until that time, as in humans, ultrasound is used to diagnose PKD in cats. Dr. Lyons spoke of her work at NIH, particularly in the feline genome project. She was quite optimistic that a blood test could be developed for PKD since the locus of the defective gene in human PKD is so well-established. The test could be facilitated through a joint effort which would utilize the original PKD research colony of cats at Dr. Biller's lab. She suggested that blood samples taken from cats at the time of testing and sent to her at NIH, along with their pedigrees, would be invaluable for cats that test either positive or negative for PKD. These samples should be 5-10ml from an adult cat with anticoagulant in a test tube (not the red top). It should be refrigerated before shipment and sent via overnight service to: Leslie A. Lyons, PhD, National Cancer Institute, Frederick Cancer Research and Development Center, Laboratory of Genomic Diversity, Building 560, Room 11-10, Frederick, MD 21702-1201. A lively question and answer period followed Dr. Lyons' presentation, and lasted for nearly an hour. Dr. Solveig Pfleuger was in the audience and contributed much to the discussion. Dr. Pfleuger was the feline genetics consultant who advised Dr. Biller in his research project to identify mode of inheritance of PKD. We were quite pleased to be presented with a check by Dr. Linda Pollack Mercer to the Winn Foundation specifically earmarked for the "PKD Study" at the conclusion of the meeting. This is the first donation for a new fund to develop a blood test for PKD. I do hope many of you, either individually and/or through your clubs, will consider a donation to this fund. While scanning is necessary at present and for the foreseeable future, we can all work for the day when a blood test for young kittens will quickly answer the PKD question. FURTHER READING:PKD and Cats
PKD and People
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