A rare disease is something that most people would not want to have and so getting test results back from the doctor which indicate that someone has a rare disease is not something to be excited about.
Consider the statement "I'm waiting on some test results from the Dr. and it's taking forever.". Based on this "I am so excited to get my test results back from the doctor and find out that I have a rare disease." a true statement? Yes, no, or I don't know?