It states in one of the history books I'm reading (from 1973) that King James I /VI suffered from porphyria. But under further investigation, I found that the current theory
was that he suffered from mild Lesch-Nyhan Syndrome. This is a genetic disease, carried along the maternal line, which causes the build up of uric acid - and hence the withered kidney replete with kidney stones revealed at the king's autopsy. LNS also is an explanation for the king's clumsiness and why he only learnt to walk when past infancy. Although he did not seem to suffer any intellectual impairment until the final stages of his life, he was in constant abdominal pain and suffered from gout - again symptoms of mild LNS.
But King James I/VI did not
suffer from porphyria, and neither, apparently, did George III. This latter theory was postulated by a mother and son team of psychiatrists in 1968, and has subsequently been assumed to be true ever since: including the author of the book I am reading at the moment.
I have often thought that in some ways a historian who purports to write 'the truth' can, in some ways, be more deceptive than the novelist who only admits to writing fiction. Sometimes facts can be wrong in ways that fiction never can be.