This is a bit of insight to what DM means in dog's from;
Lisa G Shaffer, PhD, FACMG
Founder & CEO – Genetic Veterinary Sciences, DBA Paw Print Genetics
It is important for your customers to know that you do complete health testing, which provides you important information to produce the healthiest puppies possible. DM, like many other canine genetic diseases, is recessive, meaning that a puppy must inherit two copies of the mutation for them to be at risk of developing the disease. Knowing that a parent is a carrier with one copy of the mutation (not affected) allows you to pair that dog with another dog that is clear (has no copies of the mutation) so that no pups are ever born with two copies of the mutation, which would put them at risk. Dogs that have one copy of the mutation are simply carriers and are not at risk for developing the disease.