Autism is a disorder of neural development, which impacts the communication, behavior mood and and social skills. There is one person who will be diagnosed of autism in every twenty in the world, and in the U.S., the percent of autism is 1/1000 to 1/1500. The factor of causing autism is unsure, some researches claim the genetic factor is the primary reason that causes autism, and they even find 7 groups of gene which could possibly cause it. Also, researchers suspect vaccinations are quite important for autism, which MMR is the first suspect.
The theory of MMR causing autism was mentioned by Andrew Wakefield in 1988, but after the researches and experiment, some people believe the morbidity of autism and MMR are not related. However, later Kennedy implied that Thimerosal (a vaccine preservative with organic mercury) may causes autism, because he found that the mercury poison is very similar to autism. The controversy of vaccinations theory is never stopped, but the CDC still required medicine companies to stop using Thimerosal as vaccine preservative. There are a lots of researches showed the MMR vaccine has no connection with autism, and even after stopping use Thimerosal, the rate of autism did not drop.