Sudomotor sympathetic hypofunction in Down's syndrome

General sympathetic dysfunction has been proposed as an explanation for the inability to reach normal heightened attention in Down's syndrome (DS). The present study on 15 DS subjects (group average age +/- SD, 14.3 +/- 3.6 years; 11 males) and in an equal number of age- and gender-matched normal subjects (NS), evaluated activity in different subdivisions of the sympathetic nervous system. DS subjects had (i) lower skin conductance levels (i.e., lower sudomotor sympathetic activity) and (ii) higher heart rates than NS. In response to auditory stimuli, DS subjects showed abnormal SSR responses (also indicating sudomotor sympathetic activity) but normal cutaneous vasoconstriction. Hence the results suggest that sympathetic dysfunction in DS is restricted to the sudomotor subdivision, activity of which has been associated with attention and recognition.