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Is Schizophrenia Genetic or Environmental

Is Schizophrenia Genetic or Environmental?Many family studies have been conducted to establish that a familial association exists between these disorders and schizophrenia, but fewer twin and adoption studies have been conducted to investigate the role that genetic influences play in their etiology.

As stated earlier, different models exist to explain the genetic transmission of the liability to schizophrenia. For example, some researchers believe that a single major gene specific to schizophrenia exists, and that this liability will be expressed in alternative phenotypes, depending upon the presence or absence of other genetic potentiators and environmental stressors. An influential alternative model is the multifactorial polygenic threshold model. According to this view, there is no single gene primarily responsible for the liability to schizophrenia. Rather, a large number of vulnerability genes and environmental influences exist that contribute to an individual’s liability, and a liability threshold must be surpassed for an individual to manifest the disorder. Thus, different disorder phenotypes will be expressed by surpassing successively higher severity thresholds. Mixed models combine features of both of them. For example, a single major gene may operate in some families in addition to the polygenic effects that may be primarily responsible for the genetic liability to schizophrenia. Alternatively, several genes may be necessary but not sufficient to trigger vulnerability.

A better understanding through twin and adoption studies of the way spectrum disorders are genetically related to schizophrenia, combined with knowledge about the way these disorders aggregate in families, will help researchers decide which, if any, of these models may be correct. Knowledge of the genetic model underlying schizophrenia and the schizophrenia spectrum disorders can help significantly in guiding molecular genetic studies of these disorders.

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