My 4 year old son, has for the past 2 months been really out of control, hyper, throwing items, cussing. I am puzzled because he's been a really good listener, and usually gets very upset when my husband or I discipline him. Now, he laughs at us. The interesting part in this scenario is that my 10 year old has ADHD, oppositional defiant disorder, Bi-polar. I've been dealing with some pretty serious behavioral problems with the 10 year old, same behaviors, yelling, screaming, throwing items, very hyper. I'm bringing the 4 year old to be evaluated, but since this came on so sudden, do you think it is related to 10 year old brother's behavior?