Schizophrenia and manic-depression: separate illnesses or a continuum?

Kraepelin proposed that schizophrenia and manic-depression were distinct and separable disorders. This hypothesis has been challenged recently by proponents of the "unitary psychosis" theory which posits a continuum from unipolar to bipolar disorder, continuing through schizoaffective and schizophrenic illness. In reviewing symptom cluster data and family studies, the author suggests that there is no compelling evidence to indicate a common pathophysiology for schizophrenia and bipolar disorder. More problematic is a diagnosis of schizoaffective disorder which does not appear to be a stable clinical entity. This would suggest that schizoaffective disorder is not a true clinical syndrome but rather a phenotypic variation.