Nature, Nurture, and Attention Deficit Hyperactivity Disorder

This commentary shows that Joseph's (this issue) review of the genetics of attention deficit hyperactivity disorder (ADHD) contains errors of scientific logic and ignores much relevant research. Thus, we reject his conclusions. We also reject Joseph's approach of pitting nature against nurture as if these two facets of human life are at odds with one another. Instead, most scientists who study the genetics of psychiatric disorders embrace the idea that these disorders are influenced by both genes and environmental factors. In fact, the twin studies criticized by Joseph provide the strongest evidence that environmental risk factors play a substantial role in the etiology of ADHD. They do so by showing that when one identical twin has ADHD the risk to the co-twin is much less than 100%, a fact which can only be explained by environmental risk factors. We also reject the idea that genetic studies have hindered psychosocial research, stigmatized patients, or promoted psychopharmacologic treatments. Genetic studies have aimed at solving one part of the puzzle of ADHD. By testing a parsimonious theory, they have set the stage for gene discovery and the delineation of how genes and environment combine to cause this impairing disorder.