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| |    Causes of Autism by Robert Needlman, M.D., F.A.A.P. reviewed by Christine Barry, Ph.D. In most cases, the cause of autism is unknown. Current research points to abnormalities in the brain's structure and functioning. In the past, the awful term "refrigerator mother" was used to describe the emotional coldness that was thought to be the cause. This mistaken belief added shame to the grief mothers felt. We now know for certain that autism is not caused by mothers' emotions, or anything mothers do. Genetics plays an important role. Overall, about 1 child in 500 has autism or a closely related disorder. However, within a particular family, if one child has autism, the chances of a second child having the disorder are dramatically increased, to about 10 to 20 percent. On average, biological siblings have about half their genes in common. This is also true of non-identical twins. Identical twins, on the other hand, share all their genes. In identical twins, if one has autism, there is a 60 to 70 percent chance that the other will, too. If genes told the whole story, of course, 100 percent of these identical twins also would have autism. The fact that there are some identical twin pairs in which one has autism and the other doesn't means that there must be other causes. In many cases, however, these causes are unknown. Other causes Several different conditions that cause damage to the developing brain can result in autism. These include prenatal infections with viruses such as cytomegalogvirus (CMV) and rubella. Infection with these viruses during pregnancy is harmless if the mother has already built up immunity to them. The risk of autism and other serious problems occurs only if a woman becomes infected for the first time during pregnancy. One excellent reason for universal MMR vaccination, which includes vaccines against measles, mumps, and rubella, is that it gives rubella immunity to pregnant women, protecting their children. Other rare causes of autism are metabolic problems, such as phenylketonuria. Most of these can be detected by the filter-paper blood test that is done on all newborn infants. Early detection sometimes allows for changes in diet that can prevent the development of autism. Tuberous sclerosis, another rare disorder that can cause autism, sometimes can be detected by careful examination of the skin. Unfortunately, there is no cure. Some people with autism have abnormal brain electrical activity when hooked up to an electroencephalogram (EEG). The EEG patterns resemble patterns seen during seizures. It is possible that frequent abnormal electrical activity contributes to autism in some children, even if they do not have obvious epilepsy. At least 25 percent of children with moderate and severe mental retardation have autism-a much higher occurrence than in children in general. It makes sense that a brain abnormality that causes mental retardation also is likely to cause autism, another serious brain abnormality. According to some estimates, about 8 out of 10 children with autism also have mental retardation, and of these, two-thirds have severe retardation. However, recently we have begun to identify an increasing number of children who have high-functioning autism or Asperger disorder, and these children have normal or high general intelligence.
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