The cause of autism is unknown, but scientists believe factors of autism may include genetics, infections, and problems occurring at birth. Many of the most recent studies suggest that some people have a genetic tendency to have autism which may be passed from parents to children. Scientists are looking for different clues that show which genes contribute to increasing the vulnerability of autism. Some researchers think environmental factors may also play a role in the cause of autism. Many studies of people with autism have shown abnormalities in certain regions of the brain that suggest that autism is a result from disruption in early brain development while still in the uterus. Another theory for the cause of autism is that the body's immune system may inappropriately produce antibodies that attack the brains of children. There is also a theory that says children with autism have an abnormal timing of the growth in their brains and in early childhood the brains of autistic children grow faster and larger than those of normal children and then later on when normal children's brains get bigger and better organized the autistic kids' brains grow more slowly. Many parents believe that vaccines are the cause of autism, but there is no evidence that proves vaccines cause autism or any other type of behavioral disorder. Parents believe that there is some sort of link between measles, mumps, rubella (MMR) vaccine that causes their child to receive autism. Parents believe this because the MMR vaccine is given between the ages of 12 to 15 months and a few weeks after the vaccine many parents start noticing the symptoms of autism. Although there are many theories suggesting what causes autism but there is no absolute cause. Scientists are still looking for the cause and hopefully one day they will find the cause and a cure.