Neurophysiologic Biomarkers in Rett Syndrome

Inclusion Criteria:

1. Rett Group: Females ages 3-18 (inclusive) with a clinical diagnosis of RTT with alikely pathogenic or known pathogenic variant in MECP2.

2. Likely Rett Group: Females from 1 year to < 5 years of age with MECP2 variant ifregression 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) withno developmental or cognitive concerns as assessed using the Child/Adult BehavioralChecklist, Survey of Well-Being of Young Children (<5yo), or the Wide RangeAchievement Test-4 (>5 yo).

Exclusion Criteria:

Rett and Likely Rett Groups:

1. Presence of a duplication in MECP2 or any other identified pathogenic mutation inanother 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.