Motor symptoms of the Rett syndrome: abnormal muscle tone, posture, locomotion and stereotyped movement.

Abstract

Amongst the motor, mental, cognitive and emotional symptoms of the Rett syndrome (RS) the motor symptoms stand out as the hallmark in analyzing the essential pathophysiology. Summarizing the motor symptoms and searching into the knowledge of relevant basic sciences, this report aims at stressing the pathophysiological basis of RS which we have reported in previous studies. The core motor symptoms of RS consist of two aspects; firstly the unique developmental abnormalities of the discrepancy of crawling and walking and secondly the pathognomonic symptoms which include the abnormal muscle tone, posture, locomotion and stereotyped movement. The deranged crawling reflects the abnormal locomotive function. The primary responsible neuronal structures of the abnormal muscle tone, posture and locomotion are probably in the brainstem. Aberrantly formed neuronal structures responsible for voluntary movements and modulatory factors from the basal ganglia are the pathophysiological basis of the stereotyped movement of RS. Thus the neuronal structures that underlie the clinical characteristics of RS extend broadly from the motor neurons to the higher cortex, but involve the specific neuronal systems. The most important and primary of these specific neuronal systems are thought to be the monoaminergic systems, originating from the brainstem and midbrain. Abnormally deficient noradrenergic, serotonergic and dopaminergic systems result in the abnormal modulation of ontogeny and function of the higher and lower nervous systems. As we have already stressed, this unique putative pathophysiological basis could explain the very striking set of clinical symptoms of RS and their age dependent appearance despite the lack of major specific findings in neuropathology.