Trapped Neutrophil Syndrome (TNS), also called hereditary neutropenia, is a rare blood disease of the Border Collie affecting puppies between 2 weeks and 7 months of age. The disease is characterised by deficiency of segmented neutrophils in the blood and hyperplasia of myeloid cells in the bone marrow. As a result, the immune system becomes compromised and fails to protect against infections. The widespread nature of the disease indicates that the mutation of the gene responsible for this condition was either already present in the founder dogs used to establish the breed, or originated very early in the breed. The carrier frequency of this fatal, inherited canine disease is rather high (11.1%).4 TNS has also been associated with previous drug therapy, particularly with anti-seizure medications, and sulfa drugs.3,1
Severely affected puppies have narrowed elongated skull shape described by breeders as ferret-like. Puppies are often smaller than their litter mates and suffer from chronic infections and failure to thrive. Clinical signs may include fever, lameness, swelling of the joints, loss of appetite, and diarrhea. There is usually a good response to long-term corticosteroid treatment; however, care is required to avoid their adverse effects. It is also imperative that medications are not withdrawn abruptly, as a second remission may not always be achievable.