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ABSTRACT
In the past all psychopathologies were viewed as caused by the environment. Later on case-control and familybased studies of major psychiatric disorders found genetic associations, but in many cases these findings did not survive replications. A gene-environment approach gave new hope for possible associations. Gene environment correlations emphasized that the relationship are bidirectional. However, recent meta-analyses raised doubts about the consistency of these findings as well. The review summarizes the current view on the environmental factors in the major psychopathologies.
INTRODUCTION
The views about the role of environmental and genetic risk factors for psychopathology have changed over the years from "extreme environmentalism" through denial to the appearance of critiques of environmental risk mediation, and the concept of a single genetic cause, to the acceptance of the multi-factorial origin of psychopathology, which is the currently prevailing view (1). By agreeing with the multi -factorial origin, the importance of environmental influences was reaccepted without dismissing the genetic influences. The interest in gene-environment interaction was renewed.
Genes interact with environment at a few levels, and some authors emphasized the bilateral influence which was described as gene-environment correlations (1). Gene-environment correlations (rGE) refer to the genetic control of exposure to the environment (2). rGE are divided into "passive," "active" and "evocative" (3). Gene-environment interactions (GXE) refer to genetic differences in susceptibility to specific environmental risks. In other words, environmental pathogens cause disorder and genes influence susceptibility to pathogens (4). Therefore the relationship between genes and environment is bidirectional: organisms both impact on and are impacted by the environment (5-7). The study of endo-phenotypes instead of the external phenotypic "DSM disorder" may shed light on the difficulties in finding genetic associations in some cases (4).
Psychiatric illnesses are affected by both genetic and environmental factors. The aim of this review is to focus on the environmental effects on psychopathology.
While testing causal hypotheses for psychopathology by twin and adoption studies, a number of counter arguments to the theory of environmentally mediated risks have been raised. Among them were: Measurement issues concerning the possibility of bias resulting from retrospective recall and Bell's (5) reexamination of socialization effects, where he argued that some of the effects reflected reverse causation, namely the effects of children on their environments rather than...