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Attention deficit disorder with or without hyperactivity (ADD/ADHD) is one of the most common disorders in children. Several other troubles are associated with it, including troubles of opposition/defiance, behavioral problems, anxiety and depressive troubles and learning difficulties. The complexity of this syndrome has forced researchers to try to understand its genetic and environmental origins. Family studies of twins and of adoption show that the possibility of inheriting ADD/ADHD is approximately 0.75. Three main genes could be implicated in the development of this disorder, namely, the 5-HTT, the DRD4 and the DAT1. The family environment also seems to play a role in the development of ADD/ADHD. Psychopathologies present in the parents, their personality traits and parenting techniques seem to be different with children suffering from an ADD/ADHD and according to the trouble associated with the ADD/ADHD.