The probands were required to have combined subtype ADHD, were children aged 6–17 years (inclusive), had one or more sibling(s) in same age range, had both parents available or one parent and two or more siblings available to provide a DNA sample, an intelligence quotient above 70, were free of single-gene disorders associated with ADHD, were free of neurological disease and damage, were living at home with at least one biological parent and one full sibling and did not meet the criteria for autism or Asperger’s syndrome.
