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TNS stands for Trapped Neutrophil Syndrome.  It is an immune deficiency in Border collies.  It is an inherited disorder that is very common in all populations of Border collies with more than 10% of both working and show dogs carrying the defective gene and capable of having affected puppies.

• TNS is a condition where the bone marrow produces neutrophils but they are not released into the bloodstream. This results in an impaired immune system that cannot fight infections.

• Symptoms are variable, many of the reported TNS puppies have been born looking normal but others have been born small.

• Some puppies with TNS have been small and fine boned with narrow heads at some point but this may not be evident until approx 16 weeks.

• A common first sign is a bad reaction to vaccinations with signs of fever.

• Blood tests may show an abnormally low segmented neutrophil level but TNS can only be definitely diagnosed by bone marrow biopsy.

• Any puppy that shows any signs of infection or failure to thrive is a possible case of TNS.

• There is no cure for TNS and it appears to always be fatal eventually.  Antibiotic and steroid treatment can help affected dogs live a relatively active life.

• TNS is an autosomal recessive condition.

• The symptoms are extremely variable and will depend on the bacteria that the pup encounters. There may also be other genes that effect the disease expression.

• Some dogs do not show symptoms until later in life.  Older puppies & young adult dogs diagnosed with immune system problems may have TNS so they should also be tested with the DNA test

• There is no evidence that carriers of the TNS defect have increased immune problems.

DNA Testing

In early 2007, Jeremy Shearman in Dr Wilton’s lab, identified the genetic defect that causes TNS and developed a simple DNA test to identify carriers.  The test amplifies DNA extracted from blood or mouth (buccal) swabs using the Polymerase Chain Reaction.  The CL test in Border collies developed in Dr Wilton’s lab and CEA test from Optigen work in a similar way.  Application of the TNS test has shown that TNS is widespread through the Border collie breed (Table 1).  Proportions of TNS carriers from testing are an overestimate of the population frequency because dogs related to carriers are preferentially tested.  It is estimated that 10% to 15% of Border collies worldwide are TNS carriers.  In a randomly selected sample of Borders tested from Norway 14% carried the TNS mutation.  Testing has confirmed the TNS mutation in UK, US, Japan, Europe and Scandinavia as well as Australia and New Zealand (Table 1).

Breeders can now test for TNS before breeding to avoid mating two carriers and risk producing affected puppies.  Puppies from matings between a carrier and a TNS clear will produce (on average) half carrier pups and half clear.  Puppies can be tested at a few weeks of age from a blood spot on an FTA card (provided by Dr Wilton) or a buccal swab sample (Table 2).

Dr Wilton’s lab, where the research was done, is the only lab that can do testing currently.  Blood samples in EDTA are the preferred sample for testing.  They can be sent with request forms from within Australia and no collection kit is necessary.  Collection kits for sampling from pups, or dogs that cannot go to a vet, can be obtained by providing your postal address.  While buccal samples are easier to take than blood from pups, they are not as reliable for testing.  The sample brush (swab) must pick up enough cells from the lining of the cheek to work and there are often problems.  Blood on FTA cards can also have problems if the card is flooded with blood and overloaded.  Blood should be applied sparingly to FTA cards so that the salts on the card can preserve the DNA.

Request forms for TNS testing (available from Border Collie Health and other websites) ask for supporting evidence to confirm that the sample supplied is from the dog listed on the form.  This is usually done by a vet or club official reading a microchip or a tattoo.  Testing can be done without this (for example for puppies) but the results may not be accepted by other people.

About 4000 Border Collies have been tested so far.  The high incidence of carriers (>10%) in all lines suggests that the causative mutation goes right back to the beginning of the breed and may even be found in other collie breeds like CEA is.  For this reason, it is recommended that all lineages be tested.  Once the parents have been tested clear for TNS it is not necessary to test the pups, they can only inherit the genetic defect from a carrier parent.  Both parents of any affected dog must be carriers.  Many lines that have shown no sign of the disease may still have carriers, and this includes ISDS lines and Australian working dog lines. 

Our lab cannot give Clear by Parentage Certificates for DNA tests because we are not the holders of the registered parentage information.  In many overseas countries, the breed clubs that register the dogs maintain a database of test results, include the information on registration certificates and provide Clear by Parentage certificates for puppies of registered litters where the parents have been tested.  We could prove paternity with DNA testing using the International Society of Animal Genetics Paternity Testing markers but this would cost as much as testing the pups directly for disease.

Our lab also developed the CL test and offers DNA testing for it.  This test has been successfully applied to reduce the incidence of CL carriers in the population.  Most of the carriers identified in our research on samples submitted for TNS testing were known as CL carriers but occasional CL cases are still appearing from backyard breeders (Table 2).  It is hoped that DNA testing will also enable breeders to reduce carrier rate for TNS.  However, numbers of samples being tested are dropping off with 1930 tested in 2007 but only 700 so far in 2008.

Current research in the lab is focussing on Cerebellar Abiotrophy, which causes ataxia and has been a rare problem with several recent cases in Borders collies.  It is likely to be due to a different gene mutation than the one we are working on in kelpies where it is a common problem.  DNA testing for inherited diseases in dogs is an effective way to improve the breed by managing the breeding population and slowly removing the carriers for inherited diseases without reducing the gene pool or destroying lines that carry desired traits.

Alan Wilton

School of Biotechnology, University of NSW 2052

Email:  a.wilton@unsw.edu.au