Evidence for shared environmental contributions to attention-deficit/hyperactivity traits. A twin study

Background and objectives: Behavior-genetic analyses have shown that measurements of inattention and hyperactivity-impulsivity are genetically-influenced. In view of limited studies on ADHD (Attention deficit hyperactivity disorder) in Spanish samples, this study aims to explore the genetic architecture of ADHD symptoms; inattention and hyperactivity-impulsivity in a Spanish twin schoolchildren sample. Methods: Participants were 258 pairs of adolescent Spanish twins. Symptoms of ADHD, inattention and hyperactivity-impulsivity were assessed by means of a sub-scale of the Strengths and Difficulties Questionnaire. Univariate twin models, according to sex, were run to assess the heritability of ADHD symptoms. Results: Heritability of hyperactivity was 55% in girls, 57% in boys. Inattention showed a heritability of 26% in girls, and no genetic factors influence was found in boys. Environmental factors are prominent influences among these traits. Conclusion: Our results highlight the magnitude of environmental effects among ADHD symptoms and therefore the importance of preventive programs that may modify the expression of these traits. (c) 2019 Asociacion Universitaria de Zaragoza para el Progreso de la Psiquiatria y la Salud Mental. Published by Elsevier Espana, S.L.U. All rights reserved.