Rare Diseases Clinical Research Network: Neurophysiological Correlates

Individuals with RTT, MECP2 Dup and RTT-related disorders have significant abnormalities on a number of neurophysiological measures such as EEG and Evoked Potentials (EP). Studies in representative animal models reproduce many of these abnormalities. Little is known about the relationship between these neurophysiological findings to disease evolution, severity and specific clinical features. Therefore, it is considered likely that detailed understanding of such neurophysiological features would provide additional insight into disease pathogenesis and will lead to biomarkers of disease state and severity of different features. Consequently, specialized neurophysiological assessments will be acquired, without sedation or any other type of pharmacological manipulation, on a subset of 170 subjects: 60 RTT, 18 MECP2 Dup, 32 RTT-related disorders, and 60 age-matched typically developing controls (30 females, 30 males). Primary evaluations will include auditory ERP (AEP) and visual ERP (VEP), as well as secondary analyses of specific rhythms/band activities obtained during the ERP acquisitions (gamma band changes and frontal alpha band asymmetry). Individuals will be recruited across the spectra of ages and severity. The main goal of the project is to identify potential biomarkers that can become measures for intervention and other translational studies and, at the same time, provide insight into abnormal synaptic activity and pathogenesis of RTT, MECP2 Dup, and RTT-related disorders. Therefore, the proposed assessments will be performed in all three groups of subjects enrolled in this consortium (RTT5211): RTT, MECP2 Dup, and RTT-related disorders. Findings in each set of disorders will be linked to the objectives of the the longitudinal clinical and neurobehavioral data (RTT5211) as well as to biological factors and genotyping that may be linked to clinical severity (RTT5213). The neurophysiological parameters for RTT, MECP2 Dup, and RTT-related disorders will not only be correlated with each other but also to disease staging, overall clinical severity scores and through exploratory analyses with specific clinical features; these will be repeated up to 3 times (i.e., annual [every 10-14 month] evaluations, in the context of visits for the RTT5211 protocol) during the course of study. For this purpose, linear regression and linear mixed models will be used. Preliminary and published data indicate that RTT and MECP2 Dup have distinct patterns of cortical processing on AEP, VEP demonstrates disorder and age/disease-stage dependent changes. Phenotypic severity may be related to specific ERP parameters, as some modest effects of (severity) category of mutations were observed. In addition, the secondary analyses of specific EEG rhythms/band activities will expand our preliminary studies demonstrating alpha band asymmetry as a marker of an anxiety-like response in RTT.