Von Willebrand's Disease Type 1: Genetics, Testing, and Breeding

Type 1 von Willebrand's disease follows an inheritance pattern where a dog can be clear (no copies of the relevant gene variant), a carrier (one copy), or affected (two copies), and severity in affected dogs tends to be variable rather than uniformly severe — some affected dogs have only mildly reduced clotting factor levels and few if any noticeable bleeding issues, while others are affected more significantly. This variability is part of what distinguishes Type 1 from the more uniformly severe Type 2 and Type 3 forms.

A carrier dog typically has clotting factor levels closer to normal and usually doesn't show clinical bleeding symptoms itself, but it can still pass the gene variant on to roughly half its offspring on average. This is exactly the distinction that matters most for breeding decisions — a carrier looks and acts completely normal, which is precisely why genetic testing, not clinical observation, is the only reliable way to know a dog's actual status.

A DNA test for Type 1 von Willebrand's typically returns one of three results: clear, carrier, or affected. For a pet owner with a spayed or neutered dog, this information is mostly reassuring context — a carrier or even an affected result doesn't necessarily mean daily-life symptoms, since severity varies, though it's still worth sharing with your vet for any future procedure.

For a breeder, the result directly shapes pairing decisions: breeding two carriers risks producing affected puppies, while pairing a carrier with a clear dog can still produce carrier offspring but avoids producing affected puppies from that specific pairing. Responsible breeding programs typically test both prospective parents before a pairing and adjust plans accordingly, rather than discovering status only after puppies are born and unexpected bleeding issues show up.