Doctors have revealed the myriad causes of autism spectrum disorder, as diagnoses of the condition increase in the US.
Recent figures suggest that rates in children and adults have tripled in the past decade.
A study in JAMA Network Open found that autism diagnoses among all age groups increased 175 percent between 2011 and 2022, from 2.3 to 6.3 per 1,000 people.
And the biggest increase occurred among young adults ages 26 to 34, with a 450 percent increase.
A large body of research suggests that doctors are getting better at diagnosing the condition thanks to more screening and broader diagnostic criteria.
But other factors behind this increase are increasingly being taken into account, including environmental factors such as increased exposure to pollution and pesticides.
Dr. Cooper Stone, a psychiatrist in Philadelphia, told DailyMail.com that exposure to toxic metals, pesticides and pollution could also play a role in the surge.
He said: ‘There is a strong belief that environmental factors may be partly involved in developing this condition. Although no direct environmental causes have been linked to ASD, there are many risk factors that appear to be linked.”
Experts told DailyMail.com that autism rates could rise due to increased screening, broader definitions and environmental exposure
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According to the CDC, approximately one in 36 American children and one in 50 adults have autism.
Generally, most are diagnosed with the disorder by age five, although some can be tested as early as age two.
Children between the ages of five and eight were still the most likely group to be diagnosed, at a rate of 30 per 1,000.
The condition is characterized by repetitive behaviors, interests, and activities; deficits in social communication and social interaction; and the presence of high or low sensory sensitivity.
There is no cure, but doctors can provide therapies to help relieve symptoms.
A review published last year found that people with a genetic predisposition to autism, such as a parent with the condition, who were exposed to pollution early in life were more likely to develop autism than those exposed to less pollution.
Older research from Harvard also found that exposure to air pollution, such as particulate matter, in early childhood can increase the risk of ASD by as much as 64 percent.
In the womb, exposure to particulate matter can increase the risk of ASD by 31 percent.
An Australian study published earlier this year also found that boys exposed in utero to the endocrine-disrupting chemical Bisphenol A (BPA) were six times more likely to be diagnosed with autism before the age of 11 than boys without exposure.
That team suggested that BPA – a product that produces plastic and metal food packaging – was linked to neurological and behavioral changes linked to autism.
The US has also seen an increase in the use of synthetic pesticides, which the same say could also contribute.
The use of these chemicals has increased fiftyfold since 1950.
For example, in 1952, only one in ten corn fields used pesticides to kill pests. But by 1982, 95 percent of corn fields were using them.
Some studies show that up to 80 percent of Americans have detectable levels of pesticides in their blood.
The above graph shows the increase in autism diagnoses between 2011 and 2022 by age group, according to research published earlier this year in JAMA Network Open.
The above graph shows the gap in autism diagnoses between men and women, indicating that diagnoses in women are overtaking those in men.
Earlier this year, the EPA announced an emergency suspension of the pesticide dimethyltetrachloroterephthalate (DCPA or Dacthal) because of evidence that babies exposed to it in the womb may be born underweight and with reduced IQ and development.
A recent study also suggested that unborn babies exposed to traffic-related air pollution were more likely to be diagnosed with autism.
Moreover, a Review 2021 found that “the odds of being diagnosed with autism were 3.3 times higher in premature individuals than in the general population,” because premature babies are vulnerable to birth complications and inflammation associated with autism.
This means the increase in autism could be due to more premature babies surviving birth, as the survival rate rose from 76 percent between 2008 and 2012 to 78 percent between 2013 and 2018, according to research from the National Institutes of Health (NIH).
About one in 10 babies in the U.S. are born prematurely, meaning they are born before 37 weeks of gestation, according to the CDC.
Some experts also believe that the increase is due to doctors becoming better at recognizing and diagnosing the condition.
This also means that older people with autism may never have been properly evaluated and are only just receiving their diagnosis.
In 2013, officials at the American Psychiatric Association updated the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), which is used to diagnose mental illnesses such as anxiety, depression and bipolar disorder.
The changes combined autism, Asperger’s syndrome AND pervasive developmental disorder into one category: autism spectrum disorder.
This may have led to more children being considered autistic.
Dr. Courtney Scott, medical director of Momentum Recovery grouptold DailyMail.com: ‘The introduction of new diagnostic criteria by the DSM-5 has resulted in a significantly wider range of presentations and behaviors that clinicians associate with autism spectrum disorder (ASD).
‘This strategy is useful because it also includes milder or less typical symptoms of ASD, so that more people with this disorder who were previously likely to be missed can receive comprehensive support resources.
‘Such an increase in the number of diagnoses could also be explained to some extent by this broader perspective.’
Dr. Stone said social media sites like TikTok have brought more attention to the condition, especially among groups less likely to be diagnosed, such as adults and girls, who share symptoms they had overlooked.
He said, “While social media can be a major provider of misinformation on this topic in many cases, it still leads to more individuals seeking a diagnostic evaluation, and some portion of those individuals to receive a diagnosis.”
Last year, researchers at the University of South Carolina looked at data from 700,000 children to map counties where autism is most common.
Using this data, they found hotspots in the Southeast, the East Coast and the Northeast. Rates were particularly high in New Jersey, between 2.6 and 8.1 percent of the total child population.
Meanwhile, rates were especially low in the Texas Panhandle and Oklahoma.
The experts suggested that these areas could have a higher rate of diagnoses due to pollution from urban populations and greater access to therapists and screening programs.
While none of these studies have found a definitive cause, Dr. Scott said it could help detect and prevent the condition earlier.
He said: ‘Although no causes have been identified so far, the (study) results will help unravel the mystery of ASD and, in the long term, help formulate better ways to prevent and treat the condition.’