Free Association (the Nature Genetics blog) has published a commentary from Laura Ranum, the senior author on the recent Abraham Lincoln ataxia paper. It begins:
In 1992 I received a phone call from a neurologist with an ataxia patient that had a strong family history of the disease. Impressed upon hearing there were at least eight affected family members, I asked if I could contact the patient directly. After talking to this woman about her family history she paused and said "but you know, you really ought to talk to my mother...I think she knows of some more cousins"; the SCA5 odyssey began. I called her mother, then her mother's cousins, and their cousins. A common theme of these calls was that these family members all knew that they were related to President Lincoln, but not necessarily how they were related to each other or that there was so much ataxia in the family.