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70. Prevalence and Severity of Thought Disorder in the General Population: What Does It Mean?
Although thought disorder (TD) is a fundamental component of serious mental illness (SMI), qualitatively and quantitatively distinct TD phenotypes are associated with schizophrenia and bipolar disorder, both in patients and in their clinically unaffected biological relatives. Each TD phenotype shows relative specificity in relation to each disorder and with respect to familial aggregation. TD does occur in the general population, even one that has been screened for a personal or family history of psychosis, psychiatric hospitalization and suicide. However, when TD occurs in the general population, total TD scores are significantly lower in nonpsychiatric controls (NC) than in schizophrenia (SZ) patients and their clinically unaffected relatives (RelSZ) and the proportion of NC with no TD is significantly higher than it is in SZ and RelSZ. Similarly, TD with "SZ features" (SZTD) and deviant verbalizations (the hallmark of SZTD) are also present in the general population, but at a significantly lower rate and in lower amounts than in SZ patients and their clinically well relatives. Importantly, the SZTD phenotype shows significant heritability (higher relative risk) for SZ but not for bipolar disorder, both in patients and in clinically unaffected relatives, relative to NC despite the fact that some controls have TD. Thus, the presence of TD in NC is not sufficient to obscure the significant association of the TD phenotype with the disorder or biological risk for the disorder, or its heritability.