Scientists in the United States say they have taken a step toward developing a possible diagnostic test for chronic fatigue syndrome, a condition characterized by exhaustion and other debilitating symptoms. Researchers at Stanford University School of Medicine said a pilot study of 40 people, half of whom were healthy and half of whom had the syndrome, showed their potential biomarker test correctly identified those who were ill. Chronic fatigue syndrome (CFS), also known as myalgic encephalomyelitis or ME, is estimated to affect some 2.5 million people in the United States and as many as 17 million worldwide. Symptoms include overwhelming fatigue, joint pain, headaches and sleep problems. No cause or diagnosis has yet been established and the condition can render patients bed- or house-bound for years. The research, published Monday in the journal Proceedings of the National Academy of Sciences, analyzed blood samples from trial volunteers using a “nanoelectronic assay” …