A 17-year-old boy is brought to the mental health clinic by his parents due to their concerns about his lack of motivation, odd behaviors, verbal aggression, and social isolation. The parents report the client has had few friends since middle school. Over the last 9 months, he has gradually withdrawn from family and refuses to eat meals with them. He is experiencing increased academic difficulties. His parents are concerned about drug use, but the client reports he has only used alcohol a few times and tried marijuana one time. The client has no previous medical history and is not on any prescribed medications. The client has no past psychiatric history. While meeting privately with the psychiatric mental health nurse practitioner, the client reports that his family is out to get him, and they have been poisoning his food with a chemical substance his father obtained from a terrorist organization. His mental status exam is significant for a clear sensorium, restricted affect, tangential speech, and poor insight. Laboratory testing is normal, and urine drug screen is negative. Which is the most likely diagnosis?