Dr. Pearlson pointed out that affective disorders are likely to represent a heterogeneous group of illnesses characterized by a variety of clinical symptoms. Yet, some clinical features of affective disorders may be associated with biological markers that provide clues about etiology.

His group focused on patients with the psychotic subtype of bipolar disorder, which shows symptom overlap with schizophrenia and, like schizophrenia, has a heritable component. Moreover, psychosis has been linked with genes and chromosomal regions associated with schizophrenia. The psychotic subtype of bipolar disorders responds to antipsychotics as well as to lithium, and has been associated with increased dopamine-2 receptor binding measured by positron emission tomography.

Seeking to test the hypothesis that there is more genetic similarity between psychotic bipolar affective disorder and schizophrenia than between psychotic and non-psychotic bipolar disorder, Pearlson and colleagues studied 50 families affected by bipolar disorder. Of the total, 42 families had one or more members in the study. The sample included 6 schizoaffective manic subjects but no subjects with schizophrenia.

Magnetic resonance imaging was performed in 36 patients with psychotic bipolar disorder, 34 non-psychotic bipolar subjects, 8 subjects with sub-threshold illness, and 15 unaffected family members. Scanning was also performed in a comparison group of 40 patients with schizophrenia.

Ventricular and hippocampal abnormalities appeared similar in psychotic bipolar patients and patients with schizophrenia. The findings in non-psychotic bipolar patients were similar to those of controls and unaffected family members. Dr. Pearlson believes that his findings are consistent with a possibility that etiologic and pathophysiologic mechanisms may be similar in psychotic bipolar affective disorder and schizophrenia.