Noradrenergic and Stress-Related Etiologies of Chronic Fatigue Syndrome

Symptoms of Chronic Fatigue Syndrome (CFS) are critically important to study as patients report that these symptoms are often profoundly debilitating and an impediment to effective daily functioning as well as effective vocational and social functioning, while also contributing to a significantly increased risk of psychiatric illness and diminished quality of life. Previous Phenome-Wide Association (PheWAS) studies revealed a link between a norepinephrine transporter (NET) genetic variant and CFS. Based on the potential function of the variant and published literature, elevated norepinephrine (NE) levels may underlie at least some cluster of fatigue symptoms. Some patients may experience chronic fatigue that is due to an excess of circulating NE, and fatigue symptoms are reported by our patient population to be commonly exacerbated by stress. This study will test the hypothesis that in a subset of people with severely debilitating fatigue of long duration (\>6 months) that is worsened by stress identified through the Vanderbilt electronic health record phenotyping study, have chronic over-release of the hormone NE into the bloodstream/periphery over time that results in an overload of NE. This overload of NE causes a compensatory but deleterious effect on the brain and nervous system, including sympathetic effects and dysregulated physiologic response to stress. Thus, while numerous currently approved therapies that target NET inhibit the transporter, a drug with the opposite mechanism of action, a NET activator that would decrease circulating NE, may have efficacy in treating underlying pathophysiology of chronic fatigue. Baseline NE levels and stress-induced NE levels in patients who fulfill criteria for CFS and who self-identify with stress induced worsening fatigue, will be compared to data from normal individuals pre and post-stress. After all inclusion criteria has been confirmed, an IV will be placed for blood collection, a continuous electrocardiographic trace and blood pressure cuff will be placed on the subject's arm and finger. Subjects will undergo a posture study, autonomic reflex testing, and Stroop stress testing each followed by blood specimen collection. An optional blood draw for DNA analysis will occur after patients have been provided lunch. Questionnaires will be completed after study procedures and patients have been provided lunch. Study blood collection will total up to 28 milliliters (mL): 5 mL for cytokines, 20 mL for catecholamines, and optional 3 mL for DNA.