Schizophrenia is the commonest and most important disorder of this group. The schizophrenic disorders are characterized in general by fundamental and characteristic distortions of thinking and perception, and by inappropriate or blunted affect. Clear consciousness and intellectual capacity are usually maintained, although certain cognitive deficits may evolve in the course of time. Hallucinations, especially auditory, are common and may comment on the individual’s behaviour or thoughts.
Schizotypal disorder possesses many of the characteristic features of schizophrenic disorders and is probably genetically related to them; however, the hallucinations, delusions, and gross behavioural disturbances of schizophrenia itself are absent and so this disorder does not always come to medical attention.
Delusional disorder includes a variety of disorders in which long-standing delusions constitute the only, or the most conspicuous, clinical characteristic and which cannot be classified as organic, schizophrenic, or affective.
Schizoaffective disorders are episodic disorders in which both affective and schizophrenic symptoms areprominent within the same episode of illness, preferably simultaneously, but at least within afew days of each other.