EEG features and epilepsy in MECP2-mutated patients with the Zappella variant of Rett syndrome.

Objective: To assess the presence/absence of peculiar EEG features and epilepsy in MECP2-mutated Rett patients with the Zappella-Rett variant (Z-RTT) also known as preserved speech variant.
Methods: Retrospective analysis of 16 (age 19.4+/-8.4years; range 8-38years) MECP2 mutated Z-RTT cases, including 11 high or intermediate performance (HIP), and five low-performance (LP) patients was performed. Peculiar EEG features were analyzed as a function of the HIP or LP Z-RTT categories: (1) centro-temporal spikes, (2) multifocal EEG activity, (3) EEG encephalopathy (i.e. multifocal EEG activity associated with the presence of background slowing and diffuse slow activity), (4) spindles and K-complex. Furthermore, we assessed the occurrence of epilepsy. Correlations between electroclinical features and category of Z-RTT genotype (missense or truncation mutation) were also tested.
Results: The Z-RTT HIP group showed a very abnormal EEG (presence of centro-temporal spikes: p=0.004808), although the cases studied were not epileptogenic and did not develop encephalopathy. The LP group showed multifocal EEG activity (p=0.000229), EEG encephalopathy (p=0.000229) and epilepsy (p=0.299451). No significant differences between the prevalence of centro-temporal spikes, multifocal EEG activity, EEG encephalopathy, and epilepsy between the patients with the truncation or missense mutation were observed.
Conclusions: EEG electrophysiological patterns and epileptogenic susceptibility differ in Z-RTT according to the level of performance (i.e. HIP or LP).
Significance: These results indicate that HIP and LP Z-RTT should be considered as distinct entities, not only on a clinical basis, but also as it concerns EEG features and epileptogenic susceptibility. These results could offer support in the practical management of patients and family counseling.
(Copyright 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)