Trapped Neutrophil Syndrome
(TNS) is an hereditary disease where the bone marrow produces neutrophils (white cells) but is unable to effectively release them into the bloodstream. Affected puppies have an impaired immune system and will eventually die from infections they cannot fight.
Once thought to be rare, it is now believed that the disease goes undiagnosed for several reasons. First, not very many veterinarians know about the disease to look for it. Second, even when looking, blood counts do not always show lower than normal neutrophil (white blood cell) counts. Finally, because it is an autoimmune-deficiency disease, young puppies present a variety of symptoms depending upon what infections they fall prone to. Thus many cases are not properly diagnosed and have just been thought to be fading puppies.
Making the diagnosis even more difficult is the fact that age of onset varies depending on which infection is involved at the time. Most puppies become ill before leaving the breeder but some do not have symptoms until later. The oldest known survivor was 2 years 8 months. Most affected puppies die or are euthanized by about 4 months of age.
The research now suggests that the gene is widespread throughout the Border Collie breed, TNS cases have been positively diagnosed in Australia, Great Britain, Hungary, the Netherlands, New Zealand, and the United States. The gene is autosomal recessive, which means that both parents have to be carriers to produce an affected puppy.
You can use the above table from the CEA description as a guide and a DNA test is available through Sydney University.