I think that is somewhat common situation with Marfan Syndrome. I'm fairly familiar with it because a postdoc in my lab gave a talk about it (it was her previous research) and I don't forget things easily -- but anyways, my girlfriend - who is a transplant hepatologist - told me how in her first year of internship, one of her co-interns clearly had Marfan - she didn't say anything until a patient case came up and and she quizzed the co-intern on what underlying condition the patient had... The intern couldn't figure it out until she suggested Marfan's (and he did know what it was)... Then she pulled him aside, and suggested to him directly that he might also have the condition. He was stunned for a moment, and then proceeded to get a genetic test which confirmed her diagnosis.