Autism and related syndromes—together called autism spectrum disorders (ASDs)—have a complex array of symptoms: sensory sensitivity, social anxiety, communication difficulties, and repetitive behaviors are common. People with ASDs can range from highly functional to severely disabled.
The number of ASD diagnoses is on the rise. The U.S. Centers for Disease Control and Prevention announced in March 2014 that one out of every 68 children in the United States has some form of autism. In 2002, that number was one in 150.
The causes of ASDs are not entirely known and are likely a mixture of genetic and environmental factors. Some recent research suggests that ASDs may be the result of "patches of disorganization” in the neocortex of the brain. This altered tissue can form only while the brain is developing in the womb.
And another intriguing avenue of investigation into the rise in ASD diagnoses is the impact of inflammation on the cause and course of autism.
What Is Inflammation?
Inflammation is the body’s way of fighting attack. Ideally, when a “foreign” substance—a toxin, bacteria, or a virus—enters the body, a cascade of inflammatory chemicals and processes ramp up to fight off the invader. When the battle is over, an anti-inflammatory process begins and calms the body down again.
In some people, this process of ramping up and cooling down does not go smoothly. Those people can become stuck in a constant state of inflammation—a state of battle, in which the body produces chemicals such as cytokines. Over time, these inflammatory chemicals can damage the body.
In recent years, as with autism, diagnosis of inflammatory disease has jumped in the developed world. The causes for this increase in out-of-control immune response are still not clear, but theories include recent changes to the types of bacteria people are exposed to (known as the hygiene hypothesis). Other theories point to exposure to certain chemicals like heavy metals or estrogen-like plastics. Some blame the modern diet of processed foods.
Many of these factors have also been investigated as possible autism triggers, without conclusive results.
Inflammation and the Origin of Autism
Autism likely begins in the womb, during brain formation, and animal studies indicate that layer formation in the fetal brain may be damaged by inflammation in the mother. A study published in February 2014 followed 1.2 million pregnancies in Finland. Researchers measured the women's levels of C-reactive protein (CRP), a well-established measure of inflammation. They found that the risk of autism in the children of women with the highest levels of CRP was 43 percent higher than in those of the women with the lowest levels.
Other studies have begun to show that mothers who have certain pro-inflammatory conditions are at greater risk of having children with autism—these conditions include rheumatoid arthritis, asthma, celiac disease, diabetes, and obesity. Women with autoimmune diseases are more likely to produce "antibrain antibodies," which can attack the brain tissue of a fetus. Women who have an infection during pregnancy may also be at increased risk of having children with autism.
These studies suggest that measuring inflammation in pregnant women may help identify those children most at risk for developing an ASD and help get them early intervention.
Ongoing Inflammation in Autism
Inflammation is also an active player in the autistic brain long after birth. Brain-tissue studies of people with ASDs frequently show widespread inflammation. Patterns of elevated brain cytokines have been observed to be similar to those in autoimmune disease. Inflammatory cytokines in spinal fluid and blood are higher in people with ASDs as well.
Overactive immune systems respond aggressively to stress—flooding the body with chemical messengers. Researchers at Tufts University have proposed that in people with ASDs, this flood releases hormones that activate special cells in the brain—mast cells and microglia—that normally fight infection. Their activation results in local inflammation. Over time, this inflammation can cause damage to surrounding cells.
Up to a third of people with autism also develop seizure disorders—the rate of seizures in people with autism is 10 times higher than in the general population. Although more data is needed, some researchers have suggested that seizures in autistic individuals may have an origin in brain inflammation. Treating this inflammation may aid in better seizure control.
The long-term effects of high inflammation in people with autism are not known. Studies in animal models of autism have suggested that inflammation during development causes cognitive and behavioral changes that mimic autism.
The further study of the links between inflammation and autism may lead to identifying those infants most at risk and targeting them for help, as well as to understanding ways to reduce brain inflammation in an autistic person—and thereby lessen the severity of symptoms. Understanding the impact of inflammation on autism may also lead to new treatments for traumatic symptoms and provide a better quality of life for those with autism.