Neurophysiologic BiomarkersNeurophysiologic Biomarkers in Rett Syndrome

Inclusion Criteria:

1. Rett Group: Females ages 3-18 (inclusive) with a clinical diagnosis of RTT with a likely pathogenic or known pathogenic variant in MECP2.
2. Likely Rett Group: Females from 1 year to < 5 years of age with MECP2 variant if regression has not yet occurred or child is within 6 months of last skill loss.
3. Typically developing (TD) Group: Females age matched to RTT population (1-18) with no developmental or cognitive concerns as assessed using the Child/Adult Behavioral Checklist, Survey of Well-Being of Young Children (<5yo), or the Wide Range Achievement Test-4 (>5 yo).

Exclusion Criteria:

Rett and Likely Rett Groups:

1. Presence of a duplication in MECP2 or any other identified pathogenic mutation in another gene.
2. Active medical conditions not typically found in RTT.

Typically Developing Group:

1. Score below norms on the performance tests
2. Have a known neurological disorder (excluding migraine)
3. Being on neuroactive medications.