A gene for.: The nature of gene action in psychiatric disorders

A central phrase in the new GeneTalk is X is a gene for Y, in which X is a particular gene on the human genome and Y is a complex human disorder or trait. This article begins by sketching the historical origins of this phrase and the concept of the gene-phenotype relationship that underlies it. Five criteria are then proposed to evaluate the appropriateness of the X is a gene for Y concept: 1) strength of association, 2) specificity of relationship, 3) noncontingency of effect, 4) causal proximity of X to Y, and 5) the degree to which X is the appropriate level of explanation for Y. Evidence from psychiatric genetics is then reviewed that address each of these criteria. The concept of a gene for... is best understood as deriving from preformationist developmental theory in which genes - like preformationist anlagen - code for traits in a simple, direct, and powerful way. However, the genetic contribution to psychiatric disorders fails to meet any of the five criteria for the concept of X is a gene for Y. The impact of individual genes on risk for psychiatric illness is small, often nonspecific, and embedded in complex causal pathways. The phrase a gene for... and the preformationist concept of gene action that underlies it are inappropriate for psychiatric disorders.