Rett Syndrome is a neurodevelopmental disorder that appears in girls during infancy or early childhood. It is caused by mutations in the MECP2 gene and causes girls to lose skills like walking, communicating, and using their hands. It progresses through four stages - early onset, rapid destruction, plateau, and late motor deterioration. Diagnosis involves physical exams, genetic testing, and ruling out other conditions. While there is no cure, treatment focuses on physical, occupational, speech, and behavioral therapies to support skills and development.