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Understanding Autism (page 2)

By — Helpguide
Updated on Feb 18, 2011

One Baby's Story

Melanie is a healthy one-year-old, but her parents are worried because she’s not doing many things that her older brother did at her age. When he was one, Melanie’s brother loved to play peek-a-boo and mimic his mom’s expressions and gestures. Melanie, on the other hand, rarely makes eye contact or responds when her parents call her name. Furthermore, she doesn’t babble or make other baby noises. Her mom and dad try to engage her with toys, songs, and games, but nothing they do gets her interest, let alone a laugh or a smile.

Melanie’s parents have been waiting for her to catch up, but the gap between her and others her age is only getting wider. Last week, Melanie and her mom went to the zoo with some families from the neighborhood. The other babies pointed excitedly at the animals and stared in wide-eyed wonder, but Melanie didn’t pay any attention to either the exotic animals or the other group members. At the end of the day, one of the kids banged his knee and started crying. The other babies looked distressed and many started crying themselves. Melanie didn’t even seem to notice what was going on.

The Autism Spectrum Disorders

Autism is one of a group of developmental disorders known as the autism spectrum disorders (ASDs). All of the ASDs begin in childhood and involve delays in communication and social skills. They are known as spectrum disorders because every child on the autism spectrum is affected differently, with unique challenges, symptoms, and abilities.

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Causes of autism

The causes of autism are unknown, but most experts agree that both genetic and environmental factors are involved. One popular theory is that certain individuals are born with a genetic predisposition for autism that is then triggered by something in the environment, either while the baby is still in the womb or shortly after birth.

Genetic causes of autism

Research indicates that genes—particularly inherited genetic glitches and spontaneous DNA mutations—play a primary role in the development of autism. But no single gene is to blame. Scientists believe that at least 5 to 20 major genes are involved in autism, with many others also contributing to the risk.

The bulk of the evidence for autism’s hereditary component comes from twin studies. Multiple twin studies show that when one identical twin develops autism, the other twin will also develop the disorder approximately 9 times out of 10. In fraternal twins—who are no more genetically similar than normal siblings—the concordance rate is just 1 in 10.

Large epidemiologic studies also show that older parents are at a significantly higher risk of having autistic children. The age of the father appears to be particularly important. A recent Israeli study found that children born to fathers who were 40 or older were almost six times more likely to develop autism than the children of men younger than 30. This heightened risk is likely due to genetic mutations in sperm, which are more and more common as men age.

But while some specific chromosomal abnormalities and mutations appear to cause autism themselves, in the majority of cases, the interaction of multiple genes leads to a susceptibility to autism without directly causing it.

Environmental causes of autism

Since genes don’t completely explain autism risk or the rising number of new cases, scientists are searching for environmental explanations to fill in the blanks. The idea is that toxins, chemicals, or other harmful external elements may trigger autism, either by “turning on” or exacerbating a genetic vulnerability or independently disturbing brain development.

While considerable attention has been focused on vaccines as a possible cause of autism, a growing body of research suggests that the disorder is caused by environmental factors that occur before vaccination, and sometimes even before birth.

Evidence suggests that autism can be triggered by exposure—either during pregnancy or the early months of life­—to viral infections, pesticides, insecticides, and the prescription drugs thalidomide and valproic acid. Recent studies have also found that oxygen deprivation during delivery or fetal development can up the risk of autism.

Other environmental factors being studied include air pollution, food additives, mercury in fish, flame retardants, and certain chemicals used to make plastics and other synthetic materials. These substances are particularly dangerous to young babies, whose brains are more likely to absorb toxins and less effective at clearing them out.

Autism and vaccines

When it comes to autism, no topic is more controversial than childhood vaccinations. At the center of this controversy is thimerosal, a mercury-containing preservative once commonly used in vaccines to prevent bacterial and fungal contamination. The concern is that exposure to thimerosal may lead to mercury poisoning and autism. Scientific research, however, does not support the theory that childhood vaccinations cause autism.

Five major epidemiologic studies conducted in the U.S., the U.K., Sweden, and Denmark found that children who received vaccines containing thimerosal did not have higher rates of autism. Additionally, a major safety review by the Institute of Medicine failed to find any evidence supporting the connection. Other organizations that have concluded that vaccines are not associated with autism include the Centers for Disease Control and Prevention (CDC), the U.S. Food and Drug Administration (FDA), the American Academy of Pediatrics, and the World Health Organization.

With the exception of the flu vaccine, thimerosal is no longer used in any childhood vaccines. If you remain concerned about a possible connection between autism and mercury, you can request a thimerosal-free version of the flu vaccine from your child's pediatrician.

Early signs and symptoms of autism

Autism symptoms are usually apparent by 18 to 36 months of age, and subtle warning signs may be evident much earlier—even as early as infancy. Because early intervention makes a huge difference in minimizing the symptoms and negative impact of autism, the earlier autism is identified the better. As a parent, you’re much more likely to catch the early signs and symptoms of autism if you track your child’s development, watching out for developmental delays and red flags.

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