Depends on the mutation responsible for the associated disease. Disease causing mutations affect normal body functions in different ways. Some mutations affect puppies very early in life. For example, the mutation that causes Neonatal Encephalopathy with Seizures (NEWS) presents shortly after the puppy is born and most affected dogs do not live past 2 months. While other mutations cause progressive disease, like those responsible for Progressive Retinal Atrophy (PRA). These mutations may cause minimal signs when the dog is young but will become more significant as the dog ages. Finally, there are late onset conditions, like Lafora Disease or Degenerative Myelopathy (DM), which do not show clinical signs until a dog is in their latter third in life. Because of this broad range of presentations, a breeder should become familiar with what mutations are known to affect their breed so they can take appropriate preventative steps. Where can you go to find this information? A good starting place is with the national breed organizations followed by The Orthopedic Foundation for Animals (OFA) which consolidates health concerns for most breeds. Paw Print Genetics organizes genetic testing by breed, so you are welcome to reach out to us to inquire what mutations have been found to be of concern for your breed of dog.