Evaluation of the sympathetic nervous system in trisomy-21 (Down's syndrome)

Abstract

Dopamine-β-hydroxylase (DBH) is the enzyme which converts dopamine to norepinephrine (NE) and plasma DBH activity is diminished in patients with Down's syndrome. We have investigated sympathetic, noradrenergic neurotransmission in Down's patients by measuring plasma levels of NE and DBH in patients with trisomy-21 and their parents and comparing them to healthy volunteers of similar age. The Down's patients, like normal control subjects, responded to the stress of venipuncture and to standing with a significant increase in plasma levels of NE, indicating intact sympathetic nervous system responsivity. In fact the patients had significantly ( p < 0·05) higher circulating levels of NE while supine and standing. Despite the higher NE levels systolic blood pressure was significantly lower in the patients ( p = 0·005). Plasma DBH activity was significantly ( p < 0·005) diminished in the Down's patients when compared to their parents, to age-matched controls or adult controls. While DBH does not appear to be an index of deficient sympathetic nervous activity in Down's syndrome, it may reflect the chromosome abnormality. Despite low levels of DBH, the synthetic enzyme for NE, Down's patients have normal or increased levels of NE.