Asperger syndrome may be observed and diagnosed in early childhood. No one knows exactly what causes it, but it is thought to have a genetic cause. The part of the brain which controls a person's "social behavior" (understanding and communicating with other people) may grow or function differently in a person with Asperger syndrome. Another part of the brain that may be different is the part that controls some body movement such as balance. A person with this condition may walk or act in a clumsy way and have trouble doing body actions such as sports. They may also do physical actions repetitively, such as rocking, flapping their hands, or tapping their feet. The condition seems to run in families. Parents who have Asperger syndrome often have children who have it or another kind of autism.