Atlanta ? Chronic fatigue syndrome appears to result from something in people’s genetic makeup that reduces their ability to deal with physical and psychological stress, researchers reported Thursday.

The research is being called some of the first credible scientific evidence that genetics, when combined with stress, can bring on chronic fatigue syndrome – a condition so hard to diagnose and so poorly understood that some question whether it is even a real ailment.

Researchers said the findings could help lead to better means of diagnosing and treating chronic fatigue syndrome and predicting those who are likely to develop the disorder, which is characterized by extreme, persistent exhaustion.

The Centers for Disease Control and Prevention estimates more than 1 million Americans have the condition, with women suffering at four times the rate among men.

The research is contained in a collection of 14 articles published in this month’s issue of Pharmacogenomics, a scientific journal.