MECP2 and atypical Rett syndrome: MECP2’s importance first came to light when it was shown to map to the X-chromosome and underlie Rett syndrome, characterized by a progressive inability from 6 to 18 months of age to coordinate eye and body movements along with speech impairments, autism, and reduced lifespan in females (Amir et al, 1999; Tillotson and Bird, 2020).