An extensive study of Lincoln's medical records, and those of his family, suggests that Lincoln may have had multiple endocrine neoplasia, type 2b, a rare genetic disease. The evidence, though suggestive is equivocal, and you will have to form your own opinion. I personally entertain it as reasonable, but not conclusive. By the way, the Marfan connection has been ruled out, though MEN2b does impart a Marfan-like appearance. You should read this book, as I have:
http://www.amazon.com/Physical-Lincoln-Complete-John-Sotos/dp/1440420149/ref=sr_1_1?s=books&ie=UTF8&qid=1302228375&sr=1-1
Good question!