Trapped neutrophil syndrome (TNS) is an inherited haematological disease described in the Border Collie and in the New Zealand working breeds Huntaway and New Zealand Heading Dog. Neutrophils mature in the bone marrow but cannot leave it (they remain 'trapped'), so the blood shows neutropenia while the marrow is hyperplastic. The result is an impaired immune system with recurrent infections in puppies, of highly variable severity. DNA testing identifies carriers and makes it possible to eliminate the disease from working lines.

Described in the working Border Collie and in the Huntaway and New Zealand Heading Dog. In Border Collies from Thailand a carrier prevalence of 4 % was found (allele frequency of 2 %). Outside those populations the data are scarce (limited data). Carrier testing has substantially reduced cases.

- Smaller puppies with slow growth\n- Fever and recurrent infections from the first weeks or months\n- Chronic diarrhoea and digestive infections\n- Polyarthritis, joint effusion, intermittent lameness\n- Repeated pneumonias and abscesses\n- Characteristic elongated facies ('ferret-like')\n- Neutropenia on the blood count with bone marrow rich in myeloid precursors\n- Variable severity: some adults live with mild disease and others die or are euthanised around one year of age

TNS was described in the second half of the 1990s in working Border Collies from New Zealand and Australia as a cause of puppies with recurrent infections and unexplained neutropenia. Bone marrow studies revealed the characteristic paradox: abundant myeloid precursors with no release of neutrophils into the blood. In 2011, a candidate gene approach and linkage analysis identified the VPS13B gene (the same gene altered in human Cohen syndrome) and a 4 bp deletion in exon 19 that truncates the protein. The test was applied to the Australian and New Zealand working populations, where the disease had reached significant frequencies in specific lines.

- Test the breeding animals of the working Border Collie and of the New Zealand working breeds before the first mating\n- Never mate carrier with carrier: 25 % risk of affected puppies\n- A carrier can be mated with a clear animal, prioritising clear offspring to eliminate the allele from the line\n- Suspect TNS in puppies with repeated infections and neutropenia: request genetic testing and a bone marrow examination\n- Report the results to the breed club, especially in working populations with low genetic variability

The differential diagnosis of chronic neutropenia in the puppy includes viral infections (parvovirus, distemper), immune and drug-induced neutropenias, and cyclic haematopoiesis. The laboratory key to TNS is the combination of persistent neutropenia with myeloid hypercellularity in the marrow (myelopoiesis without release). Treatment of affected animals is supportive (antibiotics for intercurrent infections) and the prognosis depends on severity; the biochemical profile is usually normal unless there is active infection. As in any recessive disease, both parents of an affected animal are obligate carriers.

1. Shearman JR, Wilton AN. A canine model of Cohen syndrome: Trapped Neutrophil Syndrome. BMC Genomics. 2011;12:258. PMID: 21605373
2. Mizukami K, et al. Trapped neutrophil syndrome in a Border Collie dog: clinical, clinico-pathologic, and molecular findings. J Vet Med Sci. 2012;74(6):797-800. PMID: 22240985
3. Lerdkrai C, Phungphosop N. Multiplex allele-specific polymerase chain reaction-based prevalence study of canine trapped neutrophil syndrome in Thailand. Vet World. 2023;16(11):2271-2276. PMID: 38152268