Mental health articles

Genetic and Environmental Influences on Normal Range Variation and on the Disordered Extreme An emerging topic in behavior genetic studies of psychopathology is whether genetic and environmental influences are similar across the range of symptoms as for the disordered extreme, or whether the etiology of normal range variation in the trait(s) relevant to a disorder is the same as the etiology of the disorder itself.

Behavior genetic methods are beginning to be used to test contrasting models of psychopathology that regard disorders as merely the extreme of normal functioning, as opposed to categorically distinct entities. Several behavior genetic techniques have been developed to address this issue, and each of those techniques does so slightly differently. For example, one can use a multiple regression approach to test whether the genetic and environmental influences on symptoms of a disorder increase or decrease with increasing symptom levels. One can also use model fitting techniques to test whether the magnitude of genetic and environmental influences—and the best fitting etiological model—for symptoms of a disorder are the same as those on the diagnosis. The most commonly used method to address such questions is a regression-based method　which tests whether the heritability of the extreme condition (i.e., h2g), often a diagnosis, differs from the heritability of normal range variation of symptoms in the population (i.e., h2).

Unfortunately, the test of h2g–h2 tends to be very low in statistical power, as pointed out by the authors, and thus may suggest that the etiology of normal range variation in symptoms is the same as that of the disordered extreme, even in the presence of sizable differences in the two heritabilities.

Hopefully, researchers will begin to use a diversity of behavior genetic methods to address the differential etiology issue. Thus, although there is considerable interest in the use of behavior genetic methods to address such questions, a number of technical problems and conceptual issues in these analyses need to be resolved before they yield clear answers to the classificatory issues raised before.

Tags: behavior, genetics, psychological