The Marfan syndrome was found in a male descendant of Mordecai Lincoln II, great-great-grandfather of Abraham Lincoln. The common ancestry of the patient and the 16th president appears to establish genealogically that Lincoln's unusual morphological characteristics were manifestations of the genetically determined arrangement of connective tissue described by Marfan in 1896.
Schwartz H. Abraham Lincoln and the Marfan Syndrome. JAMA. 1964;187(7):473–479. doi:10.1001/jama.1964.03060200005001