Trapped Neutrophil Syndrome (TNS) An autosomal mode of inheritance is suspected – that is both parents are carriers (like C.L.)

At Massey University we have seen a number of Border Collie puppies with an intriguing illness.  These puppies, aged between 6 weeks and 7 months, have presented to us with a range of problems including lameness, chronic diarrhoea and inappetence.  All the puppies have been smaller than their litter mates and they have all had a persistent fever.  Puppies had to be euthanised due to persistent bone infections and gastro – intestinal infections.

Closed examination of these puppies have revealed very low numbers of a specific type of white blood cell, called a neutrophil, circulating in the blood. Neutrophils are predominantly responsible for destroying bacteria, therefore, a deficiency in neutrophils in circulation could result from either poor production of neutrophils (neutrophils are produced by the bone marrow) a failure of neutrophils to be released from the bone marrow into the circulation or an increased consumption of neutrophils once they are in circulation.  We considered that an increase in the rate of consumption of neutrophils was unlikely because this was a transient event in dogs and the low numbers of neutrophils in these puppies lasted for at least two weeks.  Therefore, the next step was to take samples of the bone marrow from these puppies and this confirmed that the bone marrow was producing adequate numbers of neutrophils, however the neutrophils were not being released into the circulation.  As a consequence, the bone marrow was virtually “constipated” with neutrophils.  The medical term for this condition is “myelokathexis” and it is very rare in animals and human beings.

These findings raised more questions than they answer. Why are the neutrophils apparently trapped within the bone marrow?  Is it because the membrane through which neutrophils have to migrate to get into circulation is not sufficiently permeable?  Or is it because these neutrophils are not attracted to the site of infection by factors which are released by damaged tissues?

This condition may have a genetic basis because many of these puppies are related. However, we need to see a greater number of cases before we can definitely say whether or not this condition has a hereditary basis.  We are currently conducting further work into this problem at Massey University and we would like to hear from breeders who have experienced similar problems to those outlined above.  Any information given to us would be treated with the utmost confidentiality.