This report examining a group of female schizotypal personality disorder and comparison subjects found that, contrary to predictions, the schizotypal personality disorder group did not show volume abnormalities in the superior temporal gyrus. This is not due to insufficient study group size, given the small effect size. To our knowledge, this is the first MRI study that has focused specifically on female schizotypal subjects.
Within the schizotypal personality disorder group, there was left-right difference in superior temporal gyrus volumes in those subjects with a positive family history of mental illness and a tendency for the left superior temporal gyrus gray matter volume to be smaller that was not present in those subjects who did not have a family history of mental illness. Note that the number of subjects in these two groups are small, so the data must be interpreted in that light. Moreover, most of the subjects reported a first-degree relative with affective disease, not schizophrenia, but that might be expected to dilute the finding. However no independent confirmation was available. It is possible that some of these relatives may have had comorbid schizotypal personality disorder, given the high rates of comorbidity (9
). Nonetheless, it may be that female subjects with schizotypal personality disorder and a positive family history of major mental illness may have anatomical features similar to male subjects with schizotypal personality disorder.
Of note, however, subjects with schizotypal personality disorder with more odd speech had more reduced left superior temporal gyrus volumes. The qualities of the odd speech by definition include speech that is vague or over-inclusive. In addition, pilot data suggested that female subjects with schizotypal personality disorder demonstrate formal thought disorder.
These results point to a neuroanatomical difference between male and female subjects with schizotypal personality disorder, since male subjects demonstrated frank superior temporal gyrus abnormalities (4
) whereas female subjects did not. This finding suggests that the interaction between gender and disease may play a pivotal role in the generation of abnormal brain morphometry and clinical symptoms in the schizophrenia spectrum. Similar to our data, Gur et al. (10
) demonstrated gender differences in the superior temporal gyrus in schizophrenic subjects, with female subjects exhibiting normal volumes. Bryant et al. (11
) showed a gender effect for the whole temporal lobe for male schizophrenia subjects who had reduced volumes compared with male comparison subjects, but no difference between female schizophrenia subjects and their gender-matched comparison subjects. No gender effect on superior temporal gyrus was noted, however, in that publication, although as the authors noted themselves, gray and white matter were not analyzed separately, which many consider key for the evaluation of this brain region (1
). Some of the differences in findings also may be due to the overlap of volumes between subject groups and inherent measuring difficulties due to greater variability in the surface morphometry of the superior temporal gyrus in schizophrenic subjects relative to comparison subjects (12
). Moreover, the effect of gender on the volume of superior temporal gyrus is not clear. Even within healthy nonpsychiatric populations, some investigators report a main effect of gender on the superior temporal gyrus (13
) while others do not, when using surface-based modeling approaches (14
), or when using semiautomatic volume measures (15
). Nonetheless, the current data and clinical data suggest that there is heterogeneity within the schizophrenia spectrum and that gender appears to be a critical factor in producing divergence.
Although the superior temporal gyrus was of normal volume in this group of female subjects with schizotypal personality disorder, it may not be functioning normally, as evinced by the correlation with odd speech. Functional MRI studies of this population may be an intriguing way of testing this hypothesis.