We had almost the same conversation after my nephew was diagnosed. At first nobody thought ADHD ran in our family, but once my grandmother started sharing old stories, we realized one of my uncles had many of the same traits, even if nobody recognized them back then. I found this article really helpful because it explains the genetics in an easy way and even touches on why it can seem to skip generations: is ADHD genetic from mother or father . It answered a lot of the questions we had.