I noticed at Colin Wilson World an article by Colin Wilson and Donald Leslie Hotson on a book in preparation, Will Shakespeare's hand, which - to cut to the chase - asserts definitive proof of the identities of "Mr WH" and the "dark lady" of Shakespeare's sonnets.
It isn't the first such claim, and I'm sure it won't be the last. As William Boyd describes in the Guardian - Two loves have I - the game of identifying these characters is a long-running one. It even surfaced in the Dr Who episode The Shakespeare Code, which identified the Dark Lady as Martha Jones (a nice turn on the theory that the Dark Lady was black or mixed-race). In a more literary context, the same idea is central to Anthony Burgess' Nothing Like the Sun (see the Literary Encyclopedia entry here). Written in a beautiful freewheeling English, through the device of a drunken lecturer whose descent into delirium mirrors that of Shakespeare, it focuses on Shakespeare's imagined relationship with an African prostitute in Bristol.
Nothing Like the Sun ascribes its fictionalised Shakespeare's decline and pessimism to syphilis, and this is also the thrust of Will Shakespeare's hand. This theory has a long pedigree too, although much of the evidence is speculative, based on references in Shakespeare's works. The definitive recent examination of this theory appeared in the journal Clinical Infectious Diseases in 2005: Shakespeare’s Chancre: Did the Bard Have Syphilis? by John J Ross draws on textual evidence, contemporary gossip and the detail of Shakespeare's life. A crucial indicator would be signs of poisoning from the mercury treatment for syphilis that Shakespeare was rich enough to afford. Ultimately, Ross concludes, there's no evidence of Shakespeare suffering the cognitive impairment that would accompany such poisoning, and many observed features (such as bloatedness that could be caused by kidney damage from mercury toxicity) have mundane explanations. "Perhaps Shakespeare had simply become corpulent in his retirement". And who can tell if Shakespeare's baldness was down to mercury treatment or simply male pattern baldness? (Forensics could settle this easily, if anyone was prepared to risk the curse).