In the document
Understanding and Applying ThE Genetic Test for Degenerative Myelopathy there is an interesting stat:
"For the DM test dogs coming back "At-Risk" is the probability that the dog will later develop the disease known? Are there any statistics on frequency or number seen of affected dogs in the general Chesapeake population?
As we do not know the other factors that cause the clinical onset of DM, we cannot predict what percentage of dogs testing “At-Risk” (homozygous for the susceptibility gene) will develop the disease. Dr. Coates’ research of the Veterinary Medical Database (VMDB) showed that 13 of 1,567 (0.83%) Chesapeake Bay Retrievers presenting to veterinary teaching hospitals had clinical DM. Presently, 15% of Chesapeake Bay Retrievers test “At-Risk” for DM. It is obvious that the vast majority of “At-Risk” dogs will not develop DM."