BIT-mapped somatosensory evoked potentials in the fragile X syndrome.

Middle-latency somatosensory evoked potentials (MLSEPs) were recorded from 19 scalp electrodes in ten male patients with the fragile X (fraX) syndrome and nine normal controls. One fraX patient was found presenting the so-called "giant" MLSEPs with an amplitude of N60 of about 60 microV and of 40 microV after stimulation of the right and left median nerves, respectively. Tapping of the right hand, in the same patient, induced the appearance of left parietal evoked EEG spikes. These findings further support the already suggested similarity between the epileptic picture of several fraX patients with that of the benign childhood epilepsy with centrotemporal spikes. Color mapping of the MLSEPs recorded in the remaining nine patients, when compared with the control group, showed an abnormally large N30 over the frontal regions, together with an increase in amplitude of P27, over the parietal areas, and of N60 and P100 which also presented abnormal field distributions, being represented preferentially over the frontal regions. These data could suggest the existence of a cortical dysfunction mostly involving the frontal lobes (supplementary motor area, in particular) in the fraX syndrome which could support many behavioral changes usually observed in these patients.