This is an autosomal recessive disease of Border Collies that appears to have been present in the breed for a very long time, and occurs across all lines. It is an immune defect where neutrophils are produced by the bone marrow, but there is a defect that prevents their release into the bloodstream. This results in a susceptibility to infection and tendency to ill-thrift and repeated infections. Some pups are small and fine-boned in appearance, while others appear normal. Pups will often react badly to vaccination, developing severe fever and illness. Most affected animals die or are euthanised by the age of 6 months. Affected animals are diagnosed by having a low neutrophil count on blood tests, but plentiful neutrophils on bone marrow biopsy. A DNA test is now available so that breeding animals may be tested and carrier animals detected. It is estimated that 10 – 15% of the Border collie population are carriers for trapped neutrophil syndrome. There is no cure for this disease.