A 2 year old boy was admitted for investigation of developmental retardation. He could not walk or sit independently and had started crawling just one month prior to admission. Facial features (fig. 1) included microbrachycephaly with wide mouth and protruding tongue and mandibular prognathism. Neurological examination demonstrated generalized hypotonia with trunk ataxia, severe retardation in all domains (social, gross and fine motor abilities) with lack of recognisable speech. The parents reported him as a happy child with occasional paroxysms of laughter and marked stereotypic movements. Myoclonic epilepsy with onset at 15 months was also present, with abnormal EEG findings (wide amplitude ~200 μV, rhythmic, 4–6/s, intermediate slow activity throughout the record). Magnetic resonance imaging (MRI), SE, axial T2-weighted images (TR 2100 msec, TE 90 msec) demonstrated almost symmetrical high signal abnormalities in the periventricular white matter around the occipital horns, consistent with dysmyelination (fig. 2).