Are there shared environmental influences on attention-deficit/hyperactivity disorder? Reply to Wood, Buitelaar,...

A recent large-scale meta-analysis of twin and adoption studies indicated that shared environmental influences make important contributions to most forms of child and adolescent psychopathology (Burt, 2009b). The sole exception to this robust pattern of results was observed for attention-deficit/hyperactivity disorder (ADHD), which appeared to be largely genetic (and particularly nonadditive genetic) in origin, with no observable influence of the shared environment. The central thesis of Wood, Buitelaar, Rijsdijk, Asherson, and Kuntsi [corrected] (2010) is that, contrary to these findings, shared environmental influences are important for ADHD. As evidence for this thesis, Wood et al. presented a summary of prior twin studies, followed by a discussion of 4 methodological issues that may account for my findings in Burt (2009b). I argue that, although the methodological concerns raised by Wood et al. are very important, they do not undermine my earlier results (Burt, 2009b). I close with a discussion of 2 issues that may allow for some shared environmental influences on ADHD.