Schizotypal personality disorder is quite different from the three personality disorders listed above. Classified as a Cluster A disorder, people with schizotypal personality disorder tend to be inhibited and socially withdrawn, which is in sharp contrast to people with Cluster B disorders. In general, schizotypal personality disorder is characterized by discomfort with social situations and odd, eccentric behavior.

The DSM-IV diagnosis requires five of the following nine criteria: ideas (but not delusions) of reference; odd beliefs or magical thinking (e.g., suspiciousness, telepathy); unusual bodily experiences; odd thinking and speech (e.g., vague or overelabo-rate); suspiciousness or paranoid ideation; inappropriate or constricted affect (expression of emotion); odd, eccentric or peculiar behavior or appearance; lack of close friends other than close relatives; and excessive social anxiety.

When people have ideas of reference, they believe that events in the environment pertain to them, although there is actually no connection. For example, someone might walk into a room and think everyone in the room is talking about him or her. People with schizotypal personality disorder have an elevated incidence of schizophrenia in their families, and therefore probably share some genetic loading with schizophrenia.