Sympathetic nervous system function in XYY subjects

Initial reports of males with the XYY sex chromosome anomaly indicated that these individuals excessively exhibit impulsive, aggressive, and criminal behavior. Central nervous system (CNS) defects, including low intelligence, in certain XYY subjects may be associated with these antisocial behaviors. The sympathetic nervous system (SNS) is activated in stressful conditions of "fight or flight" upon standing up from a supine posture, with physical exercise, and with aggressive behavior. Norepinephrine (NE) is the principal neurotransmitter of the SNS, and plasma levels of NE and dopamine-beta-hydroxylase are indices of SNS function. We questioned the integrity of SNS function in XYY subjects for two reasons: (1) their inferred propensity for aggressive behavior and the association of this behavior with increased NE levels; and (2) their potential for CNS dysfunction, which could be reflected in abnormal SNS regulation by the CNS. In the current study plasma levels of NE in XYY subjects are nonsignificantly higher than in normal volunteers. Additionally, XYY patients have a normal NE half-life indicating normal SNS activity and metabolism. Thus, we are unable to document with confidence any abnormality in SNS function in these XYY subjects.