A significant 2004 study by Tienari and colleagues illustrates the interplay between genetics and environment in schizophrenia. The research involved 303 adoptees, divided into a high-risk group (145 with biological mothers having schizophrenia) and a low-risk group (158 with mothers having no psychiatric history). The study also assessed whether the adoptive family environment was healthy or disturbed, with disturbed environments characterized by high levels of criticism, conflict, and poor problem-solving. The results showed that individuals with high genetic risk were far more likely to develop a psychotic disorder if raised in a disturbed environment (36.8%) compared to a healthy one (5.8%). In contrast, the rates for the low-risk group were low regardless of the environment (5.3% disturbed vs. 4.8% healthy). This demonstrates that genetic predisposition alone is not sufficient; its combination with environmental stressors is a critical factor in the development of schizophrenia.