Schizophrenia and bipolar disorder are distinguished mainly by differences in neurodevelopment.

This paper examines the commonalities and the differences between schizophrenia and bipolar disorder. Recent studies suggest a possible overlap in genetic susceptibility to the two conditions. However, while the influence of early environmental effects, particularly obstetric complications, has been established for schizophrenia, no such replicable association with bipolar disorder has been found. Structural abnormalities of the brain have been identified in both schizophrenia and bipolar disorder, but while the volume of the amygdala and hippocampus appears decreased in schizophrenia, this is not the case in bipolar disorder; indeed there are some suggestions of increased volume of the amygdala. Furthermore, schizophrenia is characterised by lower IQ, executive function and verbal memory, but there is little evidence of trait neuropsychological deficits in bipolar disorder. Similarly, premanic children do not show the cognitive and neuromotor impairments characteristic of those destined to develop schizophrenia. The most plausible explanation is that the two conditions share some genetic predisposition but differ in that schizophrenia but not bipolar disorder is subject to additional genes or early environmental hazards causing neurodevelopmental impairment.