Environmental cause is one that I am thinking makes the most sense to me. Only because of this reason. Every child that I know that was tested was severely sensitive to heavy metals, many parents are doing chelation a controversial treatment to remove heavy metals from the child. However, the kids that did get the treatment improved quite a bit. It is not recommended and like I said is still very controversial but the parents I know reported better learning and behavior skills afterwords (certainly not cured by any means) It is also very very expensive 40K and not covered by any insurance and is dangerous unless done by a well trained DAN doc.