Trapped Neutrophil Syndrome in Border Collies: Causes & Testing

Trapped neutrophil syndrome (TNS) is a fatal hereditary immune disorder that primarily affects Border collies. It occurs when the bone marrow produces neutrophils (a type of white blood cell essential for fighting infections), but a genetic mutation prevents these cells from being released into the bloodstream, leaving the immune system severely compromised.

TNS results in severe neutropenia, meaning affected dogs have dangerously low neutrophil levels, making them extremely vulnerable to infections. Puppies with TNS often show symptoms between 6 to 12 weeks old and rarely live beyond a few months, although milder cases may present later.

Understanding Trapped Neutrophil Syndrome: Causes and Symptoms

This condition is caused by an autosomal recessive mutation in the VPS13B gene. The mutation traps neutrophils inside the bone marrow, so they cannot reach the bloodstream to provide necessary immune defence.

Typical signs include poor growth, lethargy, recurrent infections involving the respiratory tract, skin, eyes, ears, diarrhoea, vomiting, and unusual physical features such as smaller size compared to littermates and a narrow, elongated skull often described as ferret-like. Some puppies may also suffer swollen joints, lameness, or painful inflammation known as hypertrophic osteodystrophy.

Which Dogs Are Affected?

TNS is breed-specific, with Border collies being most at risk. The gene mutation is found in about 7% of Border collies, which means responsible breeders need to be vigilant with testing to avoid passing the condition on.

The Genetics of TNS: How Does Inheritance Work?

TNS follows an autosomal recessive inheritance pattern. Dogs can be:

Clear – no mutation, cannot pass the gene.
Carrier – carry one copy of the mutation but do not show symptoms themselves.
Affected – carry two copies and show clinical signs.

Breeding combinations result in different likelihoods of puppies being affected, carriers, or clear, so genetic testing of breeding dogs is essential to avoid producing affected puppies.

Getting Your Dog Tested for TNS

Testing is crucial if you own a Border collie or plan to breed one. Your vet can collect a DNA sample (usually a cheek swab or blood), which is sent to an accredited laboratory such as those approved by The Kennel Club. Results will indicate whether your dog is clear, carrier, or affected.

Why Responsible Breeding Matters

Since there is no cure for trapped neutrophil syndrome and affected puppies often do not survive past a few months, preventing the condition through careful breeding decisions is the best protection. Responsible breeders test their dogs, avoid carrier-to-carrier pairings, and aim to reduce the frequency of this mutation in the Border collie gene pool.

For prospective buyers, it is wise to inquire about health testing to ensure you get a healthy puppy from breeders who prioritise genetic health.

Summary and Next Steps

Trapped neutrophil syndrome is a serious genetic disorder affecting Border collies that leads to immune deficiency and early death. Understanding the symptoms, genetics, and importance of DNA testing helps breeders and owners make informed choices to protect the breed's future health.

If you have a Border collie or are planning to get one, discuss TNS testing with your vet and work with reputable breeders who conduct responsible health screening.