RTT is notable for the variety of different behaviors it affects: disease-causing MECP2 mutations cause a rapidly fatal neonatal encephalopathy in human males but allow females to develop normally until around one year of age, at which point they regress developmentally, losing acquired language, social, and motor milestones, and instead develop ataxia, seizures, hand stereotypies, learning and memory deficits, and respiratory abnormalities (Trevathan and Naidu, 1988). The gene discussed is MECP2; the disease is cerebellar ataxia.