Purple Secret, published by Transworld Publishers on 9 July, charts the terrible path of the rare and incurable blood disease known as porphyria.
The book's writing team, comprising two molecular biologists and an historian, follows the damaging gene down through the European royal dynasties before concluding that the current Queen's late first cousin William, was also a sufferer.
Prince William, who died in a plane crash in 1972 at the age of 31, was the elder son of Henry, Duke of Gloucester, and Alice Montagu-Douglas- Scott.
In a scientific detective investigation, Martin Warren and David Hunt, both professors of molecular genetics at the University of London, have joined forces with the Sussex University historian John C G Rohl to examine the evidence that porphyria was the cause of George III's unusual behaviour. Their book describes how they followed the trail to the family of the German kaiser, even going so far as analyse the DNA of a great-granddaughter of Queen Victoria, buried in Poland.
Over the years historians and geneticists have argued about the nature of George III's illness. Those who accept the porphyria diagnosis have traced the symptomatic delusions and furies right back to Mary, Queen of Scots, and it was this explanation of the king's condition that informed Alan Bennett's acclaimed play, The Madness of George III.
Variegate porphyria, as it is properly known, was first put forward 30 years ago as the cause of the king's debilitating illness when an article in the British Medical Journal by Dr Ida Macalpine, her son Dr Richard Hunter and Prof Claude Rimington, discredited the view that that his four known bouts of madness were the result of a manic-depressive psychosis. Contemporary descriptions of the king's dementia, nerve pain and deep- coloured bluish urine backed up Macalpine and Hunter's contention that porphyria was the cause.
The genetic basis of a common form of variegate porphyria is now believed to be linked to a defect in an enzyme called protoporphyrinogen oxidase which is involved in the manufacture of haem, in turn a component of the blood pigment haemoglobin.
Since then fresh evidence has supported this theory. Two years ago Professor Rohl discovered a letter from Charlotte of Saxony-Meiningen, great-granddaughter of George III, to her doctor which discussed symptoms very close to those of porphyria.
The new book, which is accompanied by a one hour Channel 4 documentary to be screened on 13 July as part of the Secret History series, also discounts the rumour that Princess Margaret has been a sufferer.Reuse content