Functional evidence of brain stem immaturity in Rett syndrome.

Autonomic activity and respiration were studied in Rett syndrome (RS) and age matched controls. Breathing movements were monitored using a pletysmograph around the chest. Sympathetic activity was monitored by measuring blood pressure (BP) using the Finapres. Cardiac parasympathetic activity was monitored by measuring the cardiac response to baroreflex using the NeuroScope which outputs measure of cardiac vagal tone (CVT) in units of a linear vagal scale (LVS). Resting CVT (means +/- SEM) was 10.5 +/- 0.9 units in the LVS and BP was 94.6 +/- 6.4 mmHg in controls. The BP was 78 +/- 4.33 mmHg and CVT was 3.6 +/- 0.7 units in the LVS in girls with RS, 65% lower than in their age matched controls (p < 0.001), but equal to previously reported level in neonates. Each girl with RS had at least 6 types of breathing dysrhythmias, a sign of instability of the respiratory oscillator. The sympathetic system controlled the HR and BP smoothly during breath holding in control girls, but there were oscillations and rebounds in RS. The HR and BP were under parasympathetic influence during hyperventilation in normal girls but not in RS. The CVT was invariably withdrawn at the height of sympathetic activity during both hyperventilation and breath holding in RS, leading to sympathovagal imbalance with the risk of cardiac arrhythmias and possibly sudden death. Neonatal level of CVT, poor autonomic integration and multiple breathing dysrhythmias shows medullary immaturity in RS. It is the first demonstration of immaturity of the brain which could be used for screening in early childhood and potentially useful for diagnosis and management of RS.