An evaluation of autonomic nervous system function in patients with Prader-Willi syndrome.

OBJECTIVE

Prader-Willi syndrome (PWS) is a complex multisystem genetic disorder in which many cardinal features may have a neurologically based pathophysiology involving both the central and peripheral components of the autonomic nervous system. Autonomic nervous system function was studied noninvasively in a group of subjects with PWS and control subjects to determine whether autonomic nervous system dysfunction exists as part of the PWS.

DESIGN/SETTING: This cross-sectional study was performed in the neurophysiology laboratory at a tertiary care facility.

METHODS

Evaluation included anthropometric measurements and calculation of a body mass index (BMI). Simultaneous electrocardiography and serial recordings of pulse rate and systolic/diastolic mean arterial blood pressures during orthostatic maneuvers were taken. Pupillary response to the instillation of dilute pilocarpine and measurements of plasma norepinephrine at rest and after standing were also obtained. Results were analyzed using two-tailed t tests, Fisher exact test, analysis of variance, and analysis of covariance adjusting for age, gender, and BMI.

PATIENTS

There were 14 subjects with PWS (8 female, 6 male; aged 4 to 40 years, mean age 16 years) and 8 control subjects (4 female, 4 male; aged 5 to 37 years, mean age 19 years).

RESULTS

Abnormal findings were obtained only in subjects with PWS. Analysis of covariance adjusting for age, gender, and BMI revealed a trend for subjects with PWS to have lower resting diastolic blood pressure (P < .09) and significantly less change in diastolic blood pressure after standing (P < .02). Subjects with PWS had significantly greater BMI than did control subjects (P < .001), which correlated significantly with all pulse rate measurements where the greater the BMI the higher the pulse rate at rest (r = .25, P < .04) and the lower the pulse rate after arising from lying to standing at both 15 and 30 seconds (r = .17, P < .1; r = .55, P < .08 respectively). Pupillary constriction of 2 mm or more was seen in 7 of 14 subjects with PWS and in no control subjects (P < .004). The 30:15 R-R interval ratio was abnormal in 6 of 14 subjects with PWS and in no control subjects (P < .03).

CONCLUSIONS

These results suggest that patients with PWS have a detectable underlying autonomic dysfunction characterized principally by diminished parasympathetic nervous system activity.