Environmental Triggers for Autism Spectrum Disorder

"What might be some of the environmental factors involved with autism spectrum disorders, and how would they interplay with genetics?"

The rate of diagnosed cases of ASD level 1 (high-functioning autism) grows each year. A number of experts believe that the rising Asperger’s rate is an epidemic that will continue to grow, and they claim that the cause of autism must be environmental.

Other experts argue that the increased number of cases is not due to an epidemic, but instead due to a better understanding of how to diagnose these children with symptoms that were previously missed. Still others claim that the rate of the disorder is not growing more now and would have been larger in the past if the current diagnostic criteria were in place.

Environmental Factors—

A variety of environmental triggers is under investigation as a cause (or contributing factor) to the development of ASD and other autism spectrum disorders, especially in a genetically vulnerable youngster:

1. Mercury: A major toxin to the brain is mercury in its organic form. But according to a report published in Pediatrics, there is no evidence that kids with ASD in the U.S. have increased mercury concentrations or environmental exposures. Though many moms and dads of kids on the autism spectrum believe their youngster's condition was caused by vaccines that used to contain thimerosal (i.e., a mercury-containing preservative), the Institute of Medicine concludes there is no causal association. Even so, many Autism organizations remain convinced there is a link.

2. Gluten and Casein: Another environmental factor may be associated with gluten and/or casein consumption. A popular hypothesis follows this logic:  Wheat gluten and casein contain proteins which break down into molecules that resemble opium-like drugs. Kids on the autism spectrum have compromised digestive systems (called "leaky gut"). Leaky gut syndrome means that a child’s intestines are unusually permeable, allowing extra-large molecules (e.g., proteins) to leave the intestines. Thus, instead of simply excreting these large opium-like molecules, ASD kids absorb the molecules into their bloodstreams. The molecules travel to the brain, where they induce a state similar to that of a drug-induced "high."

When wheat and casein are removed from the diet, the youngster no longer experiences the high, and his behavior and abilities radically improve. A corollary to this hypothesis states that when a youngster's preferred diet is mostly comprised of wheat and dairy products (e.g., pizza, crackers, milk, ice cream, sandwiches, etc.), that proves that the child is addicted to the opiate-like molecules and would benefit from the GFCF diet. In any event, if your child will only eat a few foods, and these select foods involve wheat and/or dairy, then you will want to have him tested for food sensitivities.

3. Pesticides: Exposure to pesticides during pregnancy may boost risk. In a study published in Environmental Health Perspectives, researchers compared 465 kids diagnosed on the autism spectrum with nearly 7,000 “typical” kids, noting whether the mothers lived near agricultural areas using pesticides. The risk of having an autism spectrum disorder increased with the poundage of pesticides applied and with the proximity of the women's homes to the fields.

4. Organic Pollutants: Exposure to organic pollutants that have built up in the environment is another area of concern. For example, polychlorinated biphenyls or PCBs (substances previously found in electrical equipment, fluorescent lighting and other products) are no longer produced in the U.S., but linger in the environment. Particular types of PCBs are known to be developmental neurotoxins.

The Genetic-Environmental Interplay—

Researchers are focusing on how the interaction of genes and the environment play a role in autism. Among the findings so far is that the immune system functioning of the mother may play a role in the youngster's later development of an autism spectrum disorder.

Researchers took blood samples from 163 mothers – 61 had kids with an autism spectrum disorder, 62 had normally developing kids, and 40 had kids with non-autistic developmental delays. Then they isolated immune system antibodies (called IgG) from the blood of all the mothers. They took the blood samples and exposed them in the laboratory to fetal brain tissue obtained from a tissue bank. Antibodies from the mothers of kids with an autism spectrum disorder were more likely than antibodies from the other two groups to react to the fetal brain tissue. There was also a unique pattern to the reaction.

In an animal study, researchers then injected the antibodies into animals. The animals getting the IgG antibodies from mothers of kids with an autism spectrum disorder displayed abnormal behavior, while the animals given antibodies from the mothers of normally developing kids did not exhibit abnormal behaviors.

In another study, researchers found that levels of leptin (i.e., a hormone that plays a role in metabolism and weight) was much higher in kids on the autism spectrum than in normally developing kids, especially if the disorder was early in onset.

Critical Developmental Windows—

Asperger’s and other autism spectrum disorders are considered to be “developmental” disorders, meaning that disruption of specific maturational steps in the brain is thought to be prerequisite for developing the disorder. With many cases of autism spectrum disorders now routinely diagnosed before age 2, sensitive windows of developmental vulnerability must occur during the prenatal and/or early postnatal periods of development. Within those periods of development, there are likely to be narrower windows of greater risk for environmental exposures. Thus, it would seem that the prenatal and early postnatal periods should be a primary focus for risk of the disorder.

No single environmental factor explains the increased prevalence of Asperger’s or other autism spectrum disorders. While a handful of environmental risk factors have been suggested based on data from human studies and animal research, the most significant risk factors remain to be identified. The most promising risk factors identified to date fall within the categories of physical and psychological stressors, infectious agents, environmental chemicals, drugs, and dietary factors. However, the rate at which environmental risk factors for autism spectrum disorders have been identified through research has not kept pace with the emerging health threat posed by the disorder.

Additional research is needed, but perhaps more importantly, successful risk reduction techniques for autism spectrum disorders will require more extensive developmental safety testing of drugs and chemicals.

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