During the last year, Rebecca's 10-year-old son, Tyler has developed several unusual symptoms. For no apparent reason, Tyler's head will suddenly jerk, his eyes will repeatedly blink, or he will repetitively shrug his shoulders. In the past two months, Tyler's symptoms have become more frequent and intense. Additionally, Tyler's 4th grade teacher has complained that he sometimes makes clicking and grunting sounds in class, which he doesn't seem able to control. Which of the following does Tyler most likely have?