What Do We Know About the Causes?
Simply put, autism is a defect of brain development that impairs social skills. The condition can occur on a spectrum from mild to severe. Experts still don't know the cause, but there are many theories. "'We are sure that genetics plays a role," says Parents advisor Philip Landrigan, M.D., M.Sc., a pediatrician and director of the Children's Environmental Health Center at Mount Sinai Medical Center, in New York City. In fact, a new study in Pediatrics of babies who have an older sibling with autism found that nearly 19 percent of them were diagnosed with the disorder by age 3. The link was almost three times stronger for boys: Twenty-six percent of the male infants developed autism, compared with only 9 percent of female infants.
Many scientists, including Dr. Landrigan, also suspect a direct connection between a child's exposure to certain industrial chemicals, particularly in utero, and the risk of brain disorders including autism. Another possible cause: a parent's age. A study in Autism Research in 2010 found that while mothers have a steadily increasing risk of having a child with autism as they get older, the age of the fathers only seems to contribute to that risk when the mother is younger than 30. But it's possible that older parents are just more attuned to the warning signs of developmental problems in their children.
Vaccines are incorrectly believed by many to be another risk factor. A full 25 percent of parents think that some immunizations can cause autism in otherwise healthy infants, found a 2010 survey from the University of Michigan. (That may explain why nearly 10 percent of kids ages 19 to 35 months are not up to date on their immunizations.) However, at least two dozen studies in medical journals have refuted any connection between autism and vaccines -- particularly the MMR vaccine protecting against measles, mumps, and rubella.
Beyond the cause, researchers also aren't entirely sure why there seems to have been such a rise in the prevalence of the condition. But changes in how it is defined are certainly a factor. Between 1980 and 1994 the American Psychiatric Association defined three new forms of autism, including pervasive developmental disorder-not otherwise specified (PDD-NOS) and Asperger's syndrome. These changes essentially expanded the criteria. What's more, the Individuals With Disabilities Education Act of 1990 clarified the already existing federal law and specifically named autism as a category for special education, which caused an apparent jump in rates. Many kids who may previously have been labeled as learning disabled or mentally retarded are now diagnosed with autism.