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Orthostatic intolerance is a syndrome characterized by lightheadedness, fatigue, altered mentation, and syncope and associated with postural tachycardia and plasma norepinephrine concentrations that are disproportionately high in relation to sympathetic outflow. We tested the hypothesis that impaired functioning of the norepinephrine transporter contributes to the pathophysiologic mechanism of orthostatic intolerance.

In a patient with orthostatic intolerance and her relatives, we measured postural blood pressure, heart rate, plasma catecholamines, and systemic norepinephrine spillover and clearance, and we sequenced the norepinephrine-transporter gene and evaluated its function.

The patient had a high mean plasma norepinephrine concentration while standing, as compared with the mean (±SD) concentration in normal subjects (923 vs. 439±129 pg per milliliter [5.46 vs. 2 …