Thought Disorder Index of Finnish adoptees and communication deviance of their adoptive parents

Background. Diverse forms of thought disorder, as measured by the Thought D isorder Index (TDI), are found in many conditions other than schizophrenia. Certain thought disorder categories are primarily manifest during psychoti c schizophrenic episodes. The present study examined whether forms of thoug ht disorder qualify as trait indicators of vulnerability to schizophrenia i n persons who are not clinically ill, and whether these features could be l inked to genetic or environmental risk or to genotype-environment interacti ons. The Finnish Adoptive Study of Schizophrenia provided an opportunity to disentangle these issues. Methods. Rorschach records of Finnish adoptees at genetic high risk but wit hout schizophrenia-related clinical diagnoses (N = 56) and control adoptees at low genetic risk (N = 95) were blindly and reliably scored for the Thou ght Disorder Index (TDI). Communication deviance (CD), a measure of the rea ring environment, was independently obtained from the adoptive parents. Results. The differences in total TDI between high-risk and control adoptee s were not statistically significant. However, TDI subscales for Fluid Thin king and Idiosyncratic Verbalization were more frequent in high-risk adopte es. When Rorschach CD of the adoptive rearing parents was introduced as a c ontinuous predictor variable, the odds ratio for the Idiosyncratic Verbaliz ation component of the TDI of the high-risk adoptees was significantly high er than for the control adoptees. Conclusions. Specific categories of subsyndromal thought disorder appear to qualify as vulnerability indicators for schizophrenia. Genetic risk and re aring-parent communication patterns significantly interact as a joint effec t that differentiates adopted-away offspring of schizophrenic mothers from control adopted-away offspring.