Trapped Neutrophil Syndrome in Border Collies: Causes & Testing

Trapped Neutrophil Syndrome (TNS) is a life-threatening inherited immune disorder found mainly in Border Collies. It happens when the bone marrow produces neutrophils—white blood cells vital for fighting infections—but a genetic mutation stops these cells from entering the bloodstream, severely weakening the immune system.

The syndrome leads to severe neutropenia, where affected dogs have dangerously low neutrophil counts, leaving them highly susceptible to infections. Symptoms usually appear in puppies between 6 to 12 weeks old, and sadly, most affected dogs do not survive past the first few months. Some less severe cases may develop symptoms later in life.

What Causes Trapped Neutrophil Syndrome and What Are the Symptoms?

TNS is caused by an autosomal recessive mutation in the VPS13B gene. This mutation traps neutrophils within the bone marrow, preventing them from reaching the bloodstream to defend the body against infections.

Common signs include poor growth, lethargy, repeated infections affecting the respiratory system, skin, eyes, ears, diarrhea, vomiting, and distinctive physical traits such as a smaller size compared to siblings and an unusually narrow, elongated skull, often likened to a ferret’s head. Some puppies might experience swollen joints, lameness, or painful bone inflammation called hypertrophic osteodystrophy.

Which Dogs Are Most at Risk?

TNS primarily affects Border Collies in the U.S. About 7% of these dogs carry the gene mutation, making it essential for breeders to perform genetic testing to prevent passing this disorder to puppies.

How Does TNS Heredity Work?

This syndrome follows an autosomal recessive inheritance pattern, meaning:

• Clear: Dogs have no mutation and cannot pass the gene to their offspring.
• Carrier: Dogs carry one copy of the mutation but do not show symptoms.
• Affected: Dogs have two copies of the mutated gene and exhibit clinical symptoms.

These genetic combinations impact the likelihood of puppies being affected, carriers, or clear, highlighting the importance of testing all breeding dogs.

Testing Your Border Collie for TNS in the U.S.

If you own or plan to breed a Border Collie, testing is critical. U.S. veterinary clinics can collect DNA samples, often using a cheek swab or blood sample, which are sent to accredited laboratories such as the Veterinary Genetics Laboratory at UC Davis. Results classify dogs as clear, carriers, or affected.

The Importance of Responsible Breeding

There is no cure for trapped neutrophil syndrome, and puppies with this condition often do not survive more than a few months without intensive medical care. The best defense is preventing the disorder through careful breeding practices. Responsible breeders screen for TNS, avoid breeding two carriers together, and work to reduce the incidence of this mutation within the Border Collie population.

Prospective buyers should always ask breeders about genetic testing to ensure puppies come from healthy stock prioritized for genetic health.

In Summary: Protecting Your Border Collie’s Health

Trapped Neutrophil Syndrome is a serious genetic disease impacting Border Collies that causes immune system failure and early death. Understanding its symptoms, inheritance, and the vital role of DNA testing helps breeders and owners make well-informed choices to safeguard the breed’s future health.

If you have a Border Collie or are considering adding one to your family, talk to your veterinarian about TNS testing and collaborate only with responsible breeders who follow thorough health screening practices.