The aim of this study was to find potential signs of genetic vulnerability to schizophrenia. The differences between adoptees at high genetic risk for schizophrenia (their biological mother had a schizophrenia spectrum disorder) and control adoptees of non-schizophrenia spectrum biological mothers were assessed. The comparisons between these groups were based on the Minnesota Multiphasic Personality Inventory (MMPI) test's subscale scores adjusted by gender, age at MMPI assessment, age at placement into the adoptive family and social class. The subjects were a subsamples of a total of 182 tested adoptees and 136 mentally healthy adoptees in the Finnish Adoptive Family Study. The high-risk group was found to be distinguishable from the low-risk group based on deviant scores on the Hostility, Hypomania and Lie scales. These scales may measure genetic vulnerability and also possibly be indicative of psychometric deviance predicting future onset of schizophrenia.

Nature and nurture are not separate. Instead it is important to investigate the interplay between genes and environment and how they influence on another. To an important degree, genetic effects on behavior come about because they either influence the extent to which the individual is likely to be exposed to individual differences in environmental risk or they affect how susceptible the individual is to environmental adversities.

The current inability to explain or predict which genetically predisposed individuals will finally become schizophrenic has forced us to confront our ignorance of the precise mechanism and mode of the transmission of this disorder. Zubin's proposal to view the schizophrenic as a vulnerable individual who develops a temporary episode only under certain provocations can help place the controversy in proper perspective. Vulnerability (predisposition, diathesis) to schizophrenia can be defined as the individual's characteristic treshold beyond which stressful events produce decompensation manifest in the clinically diagnosable symptom picture.