Hi Lostitall, The problem is that, the cause is unknown. But not knowing the cause[yet], doesnt make anything else , the definite cause. Pretty solid evidence that mmr isn't the culprit by the way. Associations can be misleading, go back to early aids days, aids was associated with amyl nitrite[popular in gay sex], lots of people decided that was the cause. Only by rigorous scientific examination is their likely to be progress in understanding and treatment of problems such as autism.