To determine whether a dog has Down syndrome, breeders typically evaluate the skull. If it has a rounder shape than normal, there is a greater chance the dog has it. But because it’s not possible to predict what genes a puppy may inherit, some people prefer not to raise any potential problem dogs. The American Kennel Club does not require breeders to perform a DNA test before selling a puppy; however, it does require all puppies sold in its member countries to be tested for certain genetic diseases, including those that affect brain development.