<qa>  What is the first sign of RTT?RTT is a brain disorder that causes problems with childhood development. It is usually caused by an abnormality mutation in the gene MECP2. RTT can cause severe impairments in movement and communication skills, including speech and social interaction. The first signs of RTT include loss of acquired speech and loss of purposeful hand use for activities such as eating or playing. Individuals may also develop abnormal walking, repetitive hand movements, such as clapping or wringing, and abnormal breathing while awake. 