Many such cases

Gore Vidal theorized that Lincoln gave syphilis to Mary Todd and that's why she went "mad" and some of their children died young. To be fair the anti-Mary Todd stuff was probably misogyny and everyone's children died young in the 19th century.

Edit - Vidal in the NYRB:

No, there is no existing Wasserman report or its equivalent. But there is the well-known testimony of William Herndon, Lincoln’s law partner, that Lincoln told him that he had contracted syphilis in his youth and that it had “clung to him.” This is a primary source not to be dismissed lightly; yet Mr. Oates was quoted in the press as saying that there was never any evidence that Lincoln had had syphilis, ignoring Lincoln’s own words to Herndon. It was Newsweek, not I, who said that Mr. Vidal is a better historian than Mr. Oates. I have no opinion in the matter as I’ve never read Oates except on the subject of me, where he is bold and inaccurate.