They may develop when a child goes through a period of anxiety. There have been cases caused by certain drugs or head trauma. Tics are about three times more common in boys than in girls. They may run in families. The muscle twitching in tics repeats in the same pattern.
Tics have no apparent purpose.
They are not voluntary, but the person may be able to control them for short periods. Repressing them usually makes the person anxious until he or she develops another tic. They usually cease during sleep. They become more pronounced with tension and emotional strain. Some tics start as true spasms.