The mutation causes the dog’s infection-fighting white blood cells to be “trapped” and not released from the bone marrow. Without sufficient white blood cells in the bloodstream, the dog’s immune system is unable to fight off infections and the dog eventually dies, usually when they are a few months old. An affected puppy may not show any specific symptoms, other than susceptibility to infection, but may be smaller and less healthy than unaffected puppies. Occasionally, a dog will not show symptoms until they are older, around 7 months old. There is currently no treatment for TNS. However, the infections can be treated with antibiotics or steroids to prolong the life of the dog. It is estimated that about 10% of Border Collies are carriers of the mutation, so testing for TNS before breeding is advisable.

• Border Collie

A (CLEAR/NORMAL): These dogs have two copies of the normal gene and will neither develop Trapped Neutrophil Syndrome (TNS) nor pass this mutation to their offspring.

B (CARRIER/NOT AFFECTED): These dogs have one copy of the normal gene and one copy of the mutation associated with this disease. They will not develop Trapped Neutrophil Syndrome (TNS) due to this particular mutation and will, if bred, pass the mutation to 50% of its offspring, on average.

C (AT RISK/AFFECTED): These dogs have two copies of the mutation associated with Trapped Neutrophil Syndrome (TNS) which results in insufficient release of white blood cells, subsequent reduction in immune function and inability to fight infection.