Pastoral Breeds Health Foundation - Quarterly TNS Report - 21st May 2007

The first 3 months funding from PBHF for TNS research has allowed us to make rapid progress towards our main aims, which are to identify the TNS mutation, and to examine its distribution in Border Collies across the world, particularly in the UK.

The funding provides a Scholarship for Jeremy Shearman, which allows him to work full time on the project. In this short time he has managed to examine nearly all of the TNS gene in 2 TNS affected dogs and 2 carriers and several controls. He tested about 30,000 DNA bases that make up the functional part of the TNS gene and has found, what appears to be, the mutation that causes the disease. We need to confirm this by showing that the mutation exists in a large number of affecteds and carriers, and not in and any unaffected dogs. To do this we need to develop a cost effective, efficient test for the mutation. Once we have shown that this DNA change is the cause of TNS in all known carriers, we will check that all of the dogs predicted to carry the mutated TNS gene by our previous chromosome test really do. We will also screen samples that showed not sign of TNS to confirm that no other chromosome types identified in the original testing also carry the TNS mutation. The identification of what is very likely the TNS mutation means we can now test any dog for TNS. Dogs tested no longer have to be related to known TNS carriers.

Our continued testing of the Border Collie population worldwide has shown that TNS does occur in pure ISDS lines. A sample of 22 purely ISDS dogs from an English working farm showed 3 different lines carrying the TNS mutation. This is a carrier rate of greater than 10%. It may not be indicative of the entire ISDS population but suggests that the mutation is present at an alarmingly high frequency in ISDS dogs. It is difficult to get an unbiased estimate of the rate of TNS in ISDS lines from the samples we receive, as they are not a random sample. One way to assess the TNS carrier rate in ISDS dogs would be to test a stock of samples collected for another purpose, such as those collected for CEA testing at AHT. Such a sample group would give a good indication of the frequency of TNS in ISDS lines and which lines carry the mutation. This possible avenue of research will be investigated.

Since February, we have type 760 samples to reveal 174 carriers and 2 affecteds. Twenty-one of the carriers were from recent litters. We have identified 7 carriers from ISDS lines to date. This supports the unconfirmed TNS cases, where one parent is from ISDS lines, on the Border Collie Health Website as true TNS. Three of the tested ISDS carriers are listed on the site, UNSWIDs 1929 and 1959 and Gail Fanâ€™e Rispinge. Information on samples submitted for testing and test results are kept confidential by us and people are encouraged to publish their results on the Border Collie Health web site, so not all of the test results are generally available yet.

Testing has been difficult on a small proportion of samples. This has lead to a small number of revisions of preliminary test results. Some buccal swabs do not provide enough DNA for testing and so blood sparingly spotted onto FTA cards are preferred. FTA cards soaked in blood are not good for testing either as there is insufficient preservative. Only a small amount of blood should loaded onto FTA cards, as per instructions. Poor quality samples lead to delays in results and are much more likely to produce errors. It is hoped that the new test being developed will allow testing of even the poor samples that have been submitted.

Any samples will now be accepted for TNS testing at UNSW. Forms are available on the Border Collie Health website bordercolliehealth.com/ on the TNS page or the PBHF bulletins on the Midlands Border Collie Club site www.midlandsbordercollieclub.com/pbhf.htm . It takes 2 weeks for samples to arrive, then two to three weeks to enter into the database, run tests, and send out results by email, so plan testing accordingly. The preferred sample is blood on FTA cards, but blood in EDTA tubes can be sent if packaged properly. Mouth swabs can be sent from puppies at just a few days old but a proportion (~10%) of swabs do not work so results cannot be guaranteed and duplicate swabs are recommended.

DNA testing of genetic diseases, such as TNS, allows breeders to continue to use carrier animals in matings (if mated to TNS clear animals) and test the progeny for carrier status. This means no desired breeding lines need be lost. Over a period of several generations the disease can be eliminated from the breed by testing and selected breeding. Then testing will be no longer necessary. TNS is inherited as recessive disorder line CL and CEA. If both parents are tested clear of TNS then their progeny must be also free of the TNS mutation. In matings where one parent is a TNS carrier, about half of the pups, on average, can be expected to be carriers. In some litters all pups will be carriers and in others none will be, but each pup has a 50:50 chance of being a carrier if one parent is. For each puppy from matings between two carriers, there is a 1 in 4 chance it will be affected, a 1 in 4 chance it will be clear of TNS, and a 1 in 2 chance it will be a carrier. But such matings can result in any combination of affected, carrrier and normal pups. For example, one litter had 4 affected, 3 carriers and 1 clear puppy.

TNS has most likely been in the Border Collie breed since it origins as it occurs in several lines that are only distantly related. It occurs in show dogs originating from Australian/New Zealand, in pure English working dogs and in Australian working dogs unrelated to the show dogs. The disease can present as very different symptoms from one affected litter to another which has made it difficult to recognise as a genetic problem. It is probably the major cause of â€œfading/failingâ€� puppies. Now a DNA tests exist for TNS it can be eliminated from the breed. The purpose of this research, undertaken at University of New South Wales in Sydney, has been to assist breeders improve the health and welfare of the dogs. A side benefit is that the research could also assist in the knowledge and treatment of the disease in human patients. Discussions are in progress with medical researchers in the UK about the possible use of the Border Collie TNS to better understand the cell biology behind the disease.

Testing is currently only available at UNSW where the TNS and CL tests have been developed. The research into developing a more widely available TNS testing and determining the prevalence of TNS in the breeding population continues to be done by PhD student, Jeremy Shearman, who is supported by funds from the PBHF. Without these funds, the amazing progress Jeremy has made would not have been possible and his work could not continue.

Alan Wilton, PhD
Senior Lecturer in Genetics
Head of Canine Research Lab