[From the genetics of disease to the genetics of behavior]

Apparently a kind of antimony exists between the psychopathological approach which implies a continuum between normality and abnormality and genetic studies which intend to give a causal explanation of the mental illness. The choice of the behavioral phenotype requires nevertheless some psychopathological and clinical criteria. Furthermore, when we consider the mode of action of the genetic factor we are dealing with a behavioral target as much as with physiological mechanisms. When we discover a genetic factor in the determinism of a particular mental disorder, we must admit that the same factor is involved in the determinism of the normal behavior which corresponds to this disorder. It follows that the genetic analysis of mental illness appears as a particular methodology for the genetic approach of behavior in a general way. But it needs that we build up a new phenomenology of human behavior which fits with this approach.