Researchers have long known that caffeine helps guard against Parkinson's disease. So they have been trying to develop caffeine-like drugs that can slow the progression of the neurological disorder - without producing jittery nerves and other unwanted side effects of drinking java.
So far, however, the clinical trials have been somewhat disappointing. Now doctors know why the experimental drugs haven't worked as well as expected.
A study, released this week at the World Parkinson Congress in Glasgow, found that only about 25 per cent of Parkinson's patients carry a variation of a gene - called GRIN2A - that boosts the protective effects of coffee. One of the researchers, Haydeh Payami of the New York State Department of Health, says a genetic test could be used to identify those patients who are most likely to benefit from these therapies.