Yes its genetic. I've read a new theory that researchers have narrowed down the genetic code more closely. There is strong evidence of different brain structure and physiological differences as well.

My therapist said that Bipolar often seems to be ADHD in children and when older the mood swings become more apparent. he also said that adults with ADHD lose their hyperactivity thus, a hyperactive adult, ruling out stimulant or high caffeine use, is probably a hypomanic or manic episode. I told him without depression I'm always hyper so it must be ADHD, he said no that I just normally float on the high side. It makes sense.