Definition:

Orthostatic intolerance (OI) or postural tachycardia syndrome (POTS) is a disorder of the autonomic nervous system primarily affecting young females, and is characterized by lightheadedness, palpitations, fatigue, altered mentation, and syncope primarily occurring with upright posture and being relieved by lying down. Patients often have high plasma norepinephrine (NE) concentrations in relation to sympathetic outflow on standing. Abnormal norepinephrine transporter (NET) function is considered to contribute to the pathophysiology in some patients with OI. The impaired uptake of NE could be caused by a mutation in the SLC6A2 gene that encodes the NET.