Most doctors finally accept that chronic fatigue syndrome or ME (myalgic encephalomyelitis) does exist, even if they don't understand the cause.
So let's start with what they do know. Women are more likely than men to get the condition, it's been linked to mood disorders, sufferers are more likely to have made frequent visits to the doctor and it can be triggered by a viral infection such as Epstein-Barr virus, Q fever and viral meningitis.
So, as with the breast cancer story above, could it be that there are childhood predictors that may help us understand who is more likely to get the condition?
Researchers from the Royal Free Hospital in London found that adult ME sufferers were more likely to have a disabling illness when they were children, and who never, or rarely, played sport outside of school. But psychological problems, birth weight, birth order, atopy, obesity, school absence, academic ability or parental illness weren't predictors of the disease.
(Source: British Medical Journal, 2004; 329: 941-3).