Orthostatic intolerance and tachycardia associated with norepinephrine-transporter deficiency.
A patient with orthostatic intolerance was found to be heterozygous (had one copy of the mutant allele) for a mutation in the norepinephrine transporter gene. The mutation resulted in loss of almost all of the function of the transporter compared to the normal gene. Because the transporter is involved in clearance of norepinephrine, a mutation could lead to an increase in sympathetic activation. In other members of the patient’s family, those who had the mutation also had a greater increase in heart rate with standing and elevated plasma norepinephrine.