A pathophysiological study of neuronal ceroid lipofuscinoses in 17 patients: critical review and methodological proposal.

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The importance of visual evoked potentials (VEPs) and electroencephalography for diagnosing and distinguishing the infantile (INCL), late-infantile (LINCL) and juvenile (JNCL) forms of neuronal ceroid lipofuscinoses (NCL) is well established. Variant forms with protracted clinical courses and atypical symptoms have been described recently, whose neurophysiological characteristics sometimes overlap those of LINCL and JNCL. It is unclear whether these variant forms are due to phenotypic variability of known genetic defects, or represent new mutations. Twenty-eight NCL patients have been diagnosed at our institute; a proportion of them were investigated genetically. In 17 we performed neurophysiological investigations including VEPs, brainstem auditory (BAEP) and upper limb somatosensory (SEP) evoked potentials. We found typical and diagnostic electrophysiological involvement of the visual system in 8 patients with classic forms of NCL. Furthermore, the distinctive features of the multimodal evoked potentials in most of the six patients with variant NCL suggest that these are distinct genetic entities.