Rett Syndrome (RTT) is part of the family of Autism Spectrum Disorders. Classical RTT is a neurodevelopmental disorder clinically characterized by the initial appearance of normal early growth and development followed by a period of regression followed again by recovery or stabilization. Diagnosis is usually considered when deceleration of head growth is observed postnatally, though this may not be true in all cases. RTT patients often have partial or complete loss of acquired purposeful hand skills and/or acquired spoken language. It is also often accompanied by the advent of gait abnormalities and stereotypic hand movements 62. RTT almost exclusively affects females and is most often caused by X-linked mutations in the MECP2 gene, a transcription factor crucial to normal brain development. Rett syndrome is also associated with mutations in CDKL5 or FOXG1 though to a far lesser extent.
