Faced with the devious puzzles posed by human disease, what medical practitioner wouldn’t wish for Holmes’ powers of observation and deduction?

Arthur Conan Doyle wrote his first Sherlock Holmes tale while waiting for patients to trickle in to his fledgling medical practice on England’s southern coast; the prototype for Holmes appears to have been one of his medical school professors, famed diagnostician Joseph Bell.

More than a century later, physicians launch their investigations from a base of vastly greater medical knowledge. With modern technologies, they turn up clues unimagined in Conan Doyle’s day — a telltale quirk in a gene’s sequence, for example, or a peculiar hormonal secretion. But that doesn’t mean the mystery is gone.

Far from it. If anything, in the age of genomics the fog swirls thicker than ever.

To probe a few mysteries, read on.