Iverson's Disease was a chronic and progressive muscular disorder that affected Humans. It caused fatal degeneration of motor skills, but did not impair mental faculties. There was no known cure and no known case of remission. The exact time frame of the disease is unknown, but Jameson suffered from the disease for several years, records stating that he lost the ability to walk four years prior to his death and should never have been able to so much as lift himself from his support chair into a standard seat without help.
In 2359, Admiral Mark Jameson was diagnosed with this illness. Jameson attempted to alleviate the symptoms by using an alien drug from Cerberus II to reverse the aging process. While this appeared successful, Jameson's overuse of the drug eventually killed him. (TNG: "Too Short a Season")
In the novel Q-Space, Betazoid scientist Doctor Lem Faal was also suffering from Iverson's Disease, although unlike with Jameson his condition was depicted as having only affected his lungs and internal organs, which could be managed by medication, with no sign that he was going to suffer from physical impairment in the immediate future, although he was still concerned about his mortality.