O.S.P. Davis and colleagues at King’s College, London just published a provocative paper that aims to plot on a map of England the geographic distribution of the relative contributions of genetics and environment to 45 different childhood cognitive and behavioral traits. These traits include many that are relevant to pediatric disorders, e.g., language, the Childhood Asperger syndrome test, ADHD hyperactivity or inattention, mood swings, emotional strengths and difficulties, social or antisocial behavior, and impulsivity. They do this by making use of parental and teacher evaluations of identical and non-identical twins from over 6700 families, and noting precisely where they live. While the methodology of this analysis is much too complicated to try to explain here, you might be interested in seeing how the analysis works on an interactive map of England. The point they are making is that it matters where subjects live (or grow up) when one is evaluating the contributions of genes versus environment to their behavior. I particularly like this part of the introduction: “The second great advantage of twin and family studies is that they give us insight into the other side of the etiology of complex traits and disorders that is completely invisible to DNA microarrays and next-generation sequencing platforms: the action of the environment on variation at the population level. In the midst of the genomic revolution, it is easy to forget that even under the optimistic premise that we will eventually identify every genetic variant that influences a complex trait, we will still only know half the story of its origin, because identifying the influential environments that account for the remaining variance is just as important. This array of physical and psychosocial environmental exposures has been characterized as an ‘expososome’ that parallels the genome in its influence on complex traits.”
From the paper cited above.