Study: Autism more prevalent than thought

According to recent numbers from the Centers for Disease Control, autism is astonishingly prevalent in America’s young children, impacting one in every 36 kids, and now a new study says the number is likely even higher than that.

The study, led by Dr. Luke Grosvenor of Kaiser Permanente Northern California, puts the number at one in every 33 children age 5-8 years.

According to an original investigation published by the JAMA Network Open, “Autism Diagnosis among US children and adults, 2011-2022,” the Autism Spectrum Disorder (ASD) diagnosis rate was greatest among 5-to-8-year-olds throughout the study period and increased by 175 percent among the full sample, from 2.3 per 1000 in 2011 to 6.3 per 1000 in 2022.

Prevalence of ASD diagnosis in 2022 was highest among 5-to-8-year-olds (30.3 per 1000 children) and declined with age, the study stated, particularly among those aged 45 years or older.

“The 2022 diagnosis rate was higher among males than females at an approximately 3 to 1 ratio (9.8 per 1000 males vs 3.1 per 1000 females),” the study stated. “By race and ethnicity, prevalence was highest among Native individuals (8.1 per 1000 persons), lowest among multiracial members (3.0 per 1000 persons) and was higher among Hispanic than non-Hispanic enrollees (7.3 per 1000 persons vs 6.0 per 1000 persons, respectively).”

The cross-sectional study examined annual diagnosis rates in health records of patients in U.S. health systems from January 1, 2011, to December 31, 2022. Eligible individuals were included in the study sample for a given calendar year if they were enrolled in a participating health system for at least 10 months out of the year, the study stated, and data were extracted from 12 sites participating in the Mental Health Research Network, a consortium of research centers embedded within large, diverse health care systems.

Even with such a large cohort, the authors say their count could be low. 

“Rates reported here may underestimate the true prevalence of ASD in adults, especially older female adults, as many would not have been screened in childhood and remain undiagnosed,” the report stated. “Nevertheless, our findings indicate that the population of autistic adults in the U.S. will continue to grow, underscoring a need for expanded health care services.”

Overall trends

Though ASD prevalence in 2022 was highest among children and declined with age, the ASD diagnosis rate among all enrollees increased by 175 percent for the study period, with relative increases at each site ranging from 42 percent to 333 percent, the study stated.

“Diagnosis rates increased steadily from 2011 to 2019, with year-to-year relative increases ranging from 7.2 percent to 11.2 percent,” the researchers wrote. “Prevalence increased by just 0.6 percent from 2019 to 2020, and then increased by 16.5 percent from 2020 to 2021 and 11.9 percent from 2021 to 2022.”

The number of autistic enrollees increased at a disproportionately lower rate than the number of total enrollees from 2019 to 2020, the study found.

“We identified trends and disparities in ASD diagnosis rates among a large, diverse population of children and adults in the U.S.,” the study stated. “Rates for each year from 2011 to 2022 were highest among young children, whereas relative increases were greatest for young adults. While annual diagnosis rates were consistently higher among males, the relative increase from 2011 to 2022 was significantly greater for females, among both children and adults.”

Across racial and ethnic group strata, annual diagnosis rates tended to be highest among American Indian or Alaska Native children and adults, the study reported, while relative increases were greater within some racial and ethnic minority groups compared with white members among children, but not adults.

The researchers also said the findings should be considered in the context of past studies of ASD prevalence, including CDC Network reports of substantial increases among school-age children.

“We found increases in diagnosis rates over time across strata of age, gender, race, and ethnicity among both children and adults,” the researchers wrote. “Annual rates were highest among the youngest children, as expected based on improved early detection including universal pediatric developmental screening. Diagnosis rate increases among adults were greatest within 18-to-25 and 26-to-34-year-olds, consistent with recent findings from adult Medicaid claims data over similar periods.”

The researchers did find that male-to-female prevalence ratio among children and adults steadily declined from 2011 to 2022. 

“While this contrasts with a generally accepted notion that the 4:1 male-to-female prevalence ratio in ASD has remained stable, our findings are consistent with CDC data showing an almost 20 percent decrease among children, from 4.5:1 in 2012 to 3.8:1 in 2020,” they wrote. “Relative increases in diagnosis rates were significantly higher among female than male adults, which is in line with a 2024 report of substantial decreases in the male-to-female ratio among adults in North Carolina, from 5.6:1 in 2000 to 3.1:1 in 2021.”

The narrowing ratio could be due to better diagnosis, the researchers suggested. 

“Increased awareness of ASD presentation in females, for example related to expanded representation in social media or improved provider tools and training programs is one potential factor underlying these changes,” they wrote. “Although we could not determine age at diagnosis, multiple studies have reported increases in new diagnoses among female adults.”

The researchers did not offer an explanation for why autism rates have continued to rise, though they suggested multiple factors could be in play.

“Hypothesized reasons for prevalence increases include changes to developmental screening practices, diagnosis definitions, policies, and environmental factors as well as increased advocacy and education,” the study stated. “Prevalence estimates can also vary by case ascertainment methods or geographic region. For example, the most recent Centers for Disease Control and Prevention (CDC) Autism and Developmental Disabilities Monitoring (ADDM) Network estimates ranged from 23.1 per 1000 children in Maryland to 44.9 per 1000 in California.”

Don’t forget Toledo

Meanwhile, while Grosvenor and his team did not entertain theories as to what is causing autism, elsewhere a new study will add to the growing body of research that is exploring the interactions of genetics and environmental toxins, especially pesticides.

Dr. James Burkett, an assistant professor of neuroscience at the University of Toledo, is leading a federally funded study that will examine how pesticides may combine with genetics to increase the risk of autism.

There are hundreds of genetic variations that are associated with autism, Burkett said recently, but not everyone who has one or more of them will be diagnosed with autism.

“In very few cases can we draw a direct line from a specific genetic abnormality to an autism diagnosis,” Burkett told the University of Toledo News. “There are a lot of common genetic variants that raise the risk of autism, but those mutations don’t affect everyone in the same way. Autism is complex, and genes do not appear to be the only factor.”

Rather, Burkett’s theory is that, potentially, the chemicals children are exposed to early in their development, even while still in the womb, play a role.

Burkett said the new study, funded by the National Institutes of Health, will explore this theory by looking at what happens when animals with a gene mutation known to be a significant risk factor for autism are exposed to pyrethroids —a common class of insecticide that has itself been implicated as an autism risk factor.

“These common gene variants may be creating a genetic predisposition for autism that is then accelerated by environmental insults, like exposure to a pesticide,” he said. “This research should help us better understand how these interactions may be causing neurodevelopmental disorders.”

In a previous study in which Burkett was involved, “Developmental pyrethroid exposure causes a neurodevelopmental disorder phenotype in mice,” researchers implicated ambient exposure to pyrethroid pesticides during pregnancy in the risk for those disorders in mice.

“Low-dose developmental exposure to the pyrethroid deltamethrin (DPE) decreased pup vocalizations, increased repetitive behaviors, and impaired both fear conditioning and operant conditioning,” that study stated.

Burkett received a grant of $421,047 from the National Institute of Environmental Health Sciences for the new research, which will use prairie moles, small rodents native to the Midwest whose monogamous relationships and empathetic practices make them unusual among mammals.

“The model is really important here,” Burkett said. “Not only can we study an animal that has the same gene as humans, but we’re also studying an animal with complex social interactions. This is also an animal that naturally lives in our environment. They’re being exposed to the same things we’re exposed to. We’re interested in how it changes their behavior as well as ours.”

Richard Moore is the author of “Dark State” and may be reached at richardd3d.substack.com.