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The purpose of this study was to characterize the nature of the processes that are involved in eye tracking dysfunction (ETD). We identified a combination of quantitative measures that best distinguished qualitatively normal eye tracking from qualitatively abnormal eye tracking, using discriminant analysis. Discriminant scores distinguished schizophrenics with ETD from both schizophrenics with normal eye tracking and normal controls, but did not distinguish schizophrenics with normal eye tracking from normal controls, underscoring the heterogeneity of schizophrenic patients with respect to eye tracking. The results of the discriminant analysis indicated that ETD is a multivariate process involving a primary impairment in the smooth pursuit system characterized by increased catch-up saccades and reduced gain, and, secondarily, disinhibition of intrusive saccades, especially square-wave jerks. Quantitative characterization of ETD makes it possible to consider eye tracking as a quantitative trait in genetic investigations of a multidimensional phenotype.

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The prevalence of eye-tracking dysfunction (ETD) is significantly elevated in individuals with a diagnosis of schizophrenia and in their nonschizophrenic relatives, suggesting that ETD marks a familial (most likely genetic) risk factor for schizophrenia. Birth in a season with intemperate weather is also a widely reported risk factor for schizophrenia and is particularly marked for the subgroup with no family history of the disorder. This study examined how these two risk factors covaried in 78 patients with a Diagnostic and Statistical Manual of Mental Disorders (3rd ed., rev.; American Psychiatric Association, 1987) diagnosis of schizophrenia. Eye tracking and birth-month weather were independently assessed. As hypothesized, patients without ETD were significantly more likely to be born in months with intemperate weather (both hot and cold) than either patients with ETD or people in the general population. Etiologic factors associated with severe weather near birth may be important sources of nonfamilial schizophrenia.

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The nature of the thinking disturbances found in adolescent-onset psychotic conditions is not as well-characterized as the thought disorders found in adult psychotic patients. We used the Thought Disorder Index to examine whether schizophrenic patients in whom psychotic symptoms appear in adolescence show the same characteristic features of thought disorder as do adult schizophrenics. Quantitative and qualitative features of thought disorder were assessed in psychiatric inpatients with adolescent-onset schizophrenia, psychotic depression, and nonpsychotic conditions compared with normal control adolescents. Elevated thought disorder occurred in all groups of adolescents hospitalized for an acute episode of psychiatric illness. The magnitude of the elevation and the frequency of occurrence of disordered thinking were greatest in the psychotic adolescents. The qualitative features of the thought disturbances found in the schizophrenic adolescents were distinct from those observed in adolescents with psychotic depression. The thinking of the schizophrenic adolescents resembled that of adult schizophrenics. In both conditions thought disorder is characterized by idiosyncratic word usage, illogical reasoning, perceptual confusion, loss of realistic attunement to the task, and loosely related ideas.

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Many studies indicate that both obstetrical complications (OCs) and birth in winter or early spring are risk factors for schizophrenia, but few studies have examined how these risk factors covary in the same subjects. We assessed pre- and perinatal OCs, while blind to diagnosis, using medical data recorded at the time of subjects' births, in 29 probands with DSM-III schizophrenia or schizoaffective disorder and 39 of their unaffected adult sibs. Pre- and perinatal OCs were both significantly more common in probands than sibs. Schizophrenics not born during the winter or early spring had significantly more total and perinatal OCs than schizophrenics born in other months, but did not differ for prenatal OCs. Results indicate that OCs increase risk for schizophrenia, but also suggest the possibility that the impact of OCs on this risk may be affected by season of birth.

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Although indirect evidence suggests that obstetric complications are risk factors for bipolar disorder, few studies have directly addressed this question. Probands with bipolar disorder and their adult siblings were diagnosed according to DSM-III-R criteria by clinicians who had no knowledge of the subjects' obstetrical histories. Hospital records on gestations and births of 16 probands and 20 of their siblings without major mood disorders were scored for obstetric complications without knowledge of diagnosis. The assessment of obstetrical history was based on rating scales that have proved reliable and that reflect the number and severity of complications. Overall complication scores were significantly more severe in probands than siblings. Differences were most marked for perinatal complications.

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