Temporal lobe asymmetries as the key to the etiology of schizophrenia.

With evidence that determinants of psychosis are present early and influence brain development, and in the absence of a significant environmental contribution, schizophrenia may be regarded as a genetic encephalopathy. Morphological abnormalities are particularly apparent in the temporal lobe and on the left side of the brain, and in a number of studies significant diagnosis x side interactions have been detected. Such interactions suggest an intimate relationship between the disease process and the mechanisms that determine asymmetrical brain development. These mechanisms presumably relate to the human capacity for speech and communication, and they may have played a critical role in the evolution of the human brain. A candidate locus for an asymmetry determinant and the psychosis gene within the exchange region of the sex chromosomes is proposed. Some sex differences in schizophrenia (e.g., with respect to age of onset and brain structure) may relate to subtle differences in the rate of asymmetry development in the two sexes.