Scientists now think Chopin may have suffered from epilepsy. So, who else has been the posthumous non-beneficiary of retrospective diagnosis?
Tutankhamun: Some scientsists believe the boy Pharoa suffered from Klippel-Feil syndrome, a curvature of the spine similar to scoliosis, that would have rendered movement difficult. (Of course, others also believe he was murdered, so.)
George III: It's now believed that between the "madness," his sensitivity to light and other symptoms, the king suffered from Porphyria, a hereditary metabolic disorder caused by chemical insufficiency in hemoglobin production. This would explain his erratic behavior as well as his illness.
Abraham Lincoln has been diagnosed with a whole heap of things, mental and physical, but many believe he had the connective-tissue disorder Marfan syndrome, which would help explain his famous height. Some believe that as a result of treatment, he suffered from mercury poisoning, too.