A 9-year-old girl presents with fatigue and behavior changes. Her mother reports that she is typically very sociable but has decreased interaction with her peers and often retreats to her room. For the past 4 months or so, the patient has been irritable and angry and has become prone to acting out at home. This behavior represents a marked difference from her usual demeanor. Her performance in school also seems to be declining. The patient has no significant medical history. Her mother has a history of moderate obsessive-compulsive disorder (OCD) that was diagnosed when she was in her late 20s. The patient shows a restricted affect and monotone speech. Physical examination is otherwise unremarkable.