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orthostatic intoleranceA condition (OMIM:604715) characterised by lightheadedness, fatigue, altered mentation, syncope and tachycardia upon assuming an upright position, and markedly elevated serum norepinephrine.
Defects in SLC6A2, which encodes a member of the sodium:neurotransmitter symporter that regulates norepinephrine homeostasis, are a cause of orthostatic intolerance.
An obsolete term for neurocirculatory asthenia or effort syndrome, characterized by breathlessness, palpitation, weakness, and exhaustion.
See also: heart