Characteristics of motor disturbances of the Rett syndrome

The stereotyped movement of hands, one of the core symptoms of the Rett syndrome (RS), was analyzed to study the pathophysiology. The development of hand function was delayed after mid-infancy and handedness was undetermined in most cases. Before the onset of the pathognomonic stereotypy, patients showed excessive or abnormal behaviors of hands and mouth, such as patting or licking hands, etc. The useful hand function was lost just before or after the onset of stereotypy. The characteristic "hand wringing" movement at midline became apparent from 8 months to 3 years of age. The synchronous hand movement without reaching the midline and leg movement at midline were also seen in some patients. Based on the analysis of these symptoms, it is suggested that the stereotyped movements of RS are manifestation of fragments of normal motor behaviors at immature levels appearing excessively and repetitively with the abnormal basic posture. The pathophysiological mechanism of these characteristics is thought to be due to the hypofunctional state of the monoaminergic system from early ontogeny, which is in accordance with our previous hypothesis that RS is a developmental disorder of the monoaminergic system. The roles of the cortical involvement and sensory system are also discussed.