Early-onset encephalopathy and cortical myoclonus in a boy with MECP2 gene mutation.

The authors report the unusual clinical and neurophysiologic features of a sporadic case of a boy carrying an 806delG mutation on the MECP2 gene. A 28-month-old boy was examined for severe developmental delay, seizures, microcephaly, breathing dysfunction, and spontaneous and evoked myoclonic jerks of upper limbs. Neurophysiologic study proved the cortical origin of myoclonus; however, it was not associated with signs of cortical hyperexcitability. 3-Methoxy-4-hydroxy-phenylethylene glycol and valine concentrations were low in CSF.