PKD is an inherited kidney disease which has become very common in Persian cats and Exotic Shorthairs. Many cat breeders are aware of the problem and have been taking steps to eradicate the gene defect from their breeding lines. Up until recently the only practical way to identify the affected cats has been by ultrasound scanning of the kidneys, and the Feline Advisory Bureau established a UK PKD Ultrasound Screening Scheme for the disease in 2000. Almost 2,300 cats have been scanned in this time with an average positive result of 33 per cent.
FAB setting up PKD Negative Register
Now that a gene test is available this will most likely become the test of choice for many breeders because the sample can be taken by a local vet and kittens do not have to be ten months old before a reliable result can be obtained. However, ultrasound scanning remains a good screening test for the disease and FAB PKD Ultrasound Screening will continue to be available to breeders who prefer to use this method.
The Gene Test
The tests can be run on a blood sample, or on a sample of cheek cells (known as a buccal swab) collected by swabbing the cat’s mouth.
Cats can be tested at any age, but if pre-weaning kittens are being tested it must be done using a blood sample rather than a cheek swab. This is because nursing kittens will have traces of the queen’s DNA in their mouth, and this could cause a false test result. However, collection of cheek swabs is significantly less stressful for the cat, or kitten, than collection of a blood sample, so it may be preferable to wait until the kitten is weaned, so that testing can be done using a cheek swab.
If the sample is to be tested in this country, the swab must be sent to Langford by a vet and results should be available in about a week from the Langford Laboratory.
A note of caution: In humans there are at least six different genes that can cause different forms of PKD. It appears that autosomal dominant PKD in Persians and related breeds is all caused by one gene defect, but other forms of PKD caused by a different, unrelated gene mutation may exist.
FAB PKD Negative Register
Now that a gene test is available for polycystic kidney disease (PKD), FAB intends to set up a PKD Negative Register which can be accessed on its website (www.fabcats.org/negreg). This will allow breeders and owners to look up negative cats - useful for breeders who have prospective owners asking about the PKD status of parents or kittens and for finding breeding cats.
Cats that have been screened for PKD by either ultrasound scanning or by the gene test offered by LVD or VGL can be included in the PKD Screening Scheme, and negative cats can be listed on the FAB PKD Negative Register.
Breeders of cats which have already been scanned and found negative under the FAB PKD Ultrasound Screening Scheme will be asked if they wish their results to be included on the Register.
Cats tested negative using the DNA test can only be added if there is a valid connection between the identity of the cat and the test result - i.e. the cat’s microchip number has been written on the sample taken by a vet and the result is obviously connected to that sample. Otherwide it is not possible to ensure that a result is specific to a particular cat.
Breeders who wish their gene tested cats to be eligible for inclusion on the FAB PKD Negative Register should follow one of the procedures outlined below:
PKD Screening using the Langford Veterinary Diagnostic Laboratory at Bristol Vet School
The laboratory at Langford has kindly worked with FAB to make it as easy as possible for owners and vets to ensure that the correction information is included. Here’s what to do:
1. Download and print the LVD PKD PCR Submission form bris.ac.uk. You will need one copy of the form for each cat that is to be tested. If you do not have access to the internet, the FAB office will be happy to send you a form (call 0870 742 2278).
2. Complete Section A of the form(s).
3. Take your cat(s) to your own veterinary surgeon to be microchipped and sampled (buccal swab or blood sample). Your vet will need to complete and sign Section B of each form.
4. Your vet will submit the samples to the laboratory, and the results will be faxed and posted to the veterinary practice. Ensure that your vet passes on to you a copy of each Submission form, as well as a copy of each results form.
5. If you wish the test results to be included in the FAB PKD Screening Scheme, and any negative results to be included on the FAB PKD Negative Register, you will need to make copies of both the Submission form and the results form and submit them to the FAB, along with a cheque to cover the administration fee. The current administration fee is £4 per cat, or £3 if two or more cats owned by the same breeder are submitted at the same time.
PKD Screening using the Veterinary Genetics Laboratory in California
1. Contact the VGL www. vgl.ucdavis.edu and request a Submission form, and a buccal swab collection kit (supplied free of charge).
2. Download and print two copies of the FAB Gene Test Submission Form (www.fabcats. org) for each cat that is to be tested.
3. Complete Section 1 of all copies of the form.
4. Take your cat(s) to your own veterinary surgeon to be microchipped and sampled (buccal swab or blood sample).
5. Ensure that both copies of the FAB Gene Test Submission Form are completed for each cat, and are signed by your vet at a time that the samples are collected. One copy must be sent to the laboratory with each sample, and you should keep one copy of each form for your own records.
6. Supply your veterinary surgeon with the laboratory submission form and the postal address of the VGL.
7. Ask your veterinary surgeon to send the sample(s) on your behalf, enclosing:
A completed laboratory Submission Form
Accurately labelled samples
A completed FAB Gene Test Submission Form for each sample
A note requesting the laboratory to include the cats’ microchip numbers on their notifications of results.
6. When the test results are received, make copies of both the FAB Gene Test Submission Form and the results form for each cat.
7. If you wish the results to be included in the FAB PKD Screening Scheme, and any negative results to be included on the FAB PKD Negative Register, you will need to make copies of both the Submission Form and the results form and submit them to the FAB, along with a cheque to cover the administration fee. The current administration fee is £4 per cat, or £3 if two or more cats owned by the same breeder are submitted at the same time.
Making use of the results of a genetic test
Screening for PKD allows accurate identification of affected cats so that an informed decision can be taken as to whether or not the cat should be used for future breeding. If the cat is found to be negative then there is no problem, however if the cat is positive, a number of other factors may need to be considered.
The cat may come from a particularly valuable breeding line or it may be free of some of the other congenital or familial problems which affect Persian cats. A further concern is that by avoiding breeding from all PKD positive Persians there will inevitably be increased in-breeding between the remaining PKD negative cats.
If there are enough good reasons to use a particular affected cat for breeding, enough to outweigh the certainty that it will pass PKD on to a proportion of its offspring, then it may be appropriate to mate that cat to cat known to be free of PKD.
On average, 50% of the offspring will be affected by PKD, but a number of PKD negative kittens would also be expected and these could then be used as future breeding stock so as to maintain the desired breeding line, although there will remain the moral dilemma of what to do with the PKD positive kittens that have been produced by this mating.
