New Study Finds Genetic Risk for Autism and ADHD Declining Over Time—Raising New Questions About Environmental Exposures
A large new study published in JAMA Psychiatry has added an intriguing new dimension to the ongoing debate over the dramatic rise in autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) diagnoses.
Researchers analyzing more than two decades of data from Denmark found that individuals diagnosed with autism or ADHD in more recent years appeared to have a lower inherited genetic predisposition than those diagnosed in the 1990s. The authors concluded that expanding diagnostic criteria and changes in clinical practice likely explain much of the increase in diagnoses.
However, some scientists argue that the findings point toward a different question altogether: if genetic susceptibility appears to be declining while diagnoses continue to climb, what other factors may be contributing?
Diagnoses Rise While Genetic Risk Falls
The study, Changes in Genetic Contributions to ASD and ADHD by Year of Diagnosis, examined more than 37,000 people diagnosed with ASD or ADHD in Denmark between 1994 and 2016.
Using polygenic risk scores—an estimate of an individual’s inherited genetic susceptibility based on many genetic variants—the researchers found that people diagnosed more recently generally carried lower genetic risk scores than those diagnosed earlier.
According to the authors, these findings suggest that diagnostic practices have broadened over time, allowing individuals with milder presentations of autism or ADHD to receive diagnoses that may not have been made decades ago.
The researchers concluded that changes in diagnostic thresholds likely account for much of the increasing prevalence of ASD and ADHD.
Is Broader Diagnosis the Whole Story?
While expanded awareness and evolving diagnostic criteria have undoubtedly influenced reported prevalence, critics say the study may not fully explain the extraordinary increase in autism diagnoses observed over the past several decades.
According to the latest data from the U.S. Centers for Disease Control and Prevention (CDC), approximately 1 in 31 eight-year-old children were identified with autism spectrum disorder in 2022, continuing a decades-long upward trend.
Some researchers argue that diagnostic changes alone are unlikely to account for such a dramatic increase.
Environmental Factors Deserve Greater Attention
Scientists at Children’s Health Defense say the study raises an important question that was largely left unexplored: if inherited genetic risk appears to be decreasing over time, could growing environmental exposures be playing a larger role?
Brian Hooker, Ph.D., Chief Scientific Officer at Children’s Health Defense, believes the findings point toward a different interpretation.
“What we’re seeing instead is a lowering of the genetic threshold required to reach a toxic tipping point as the toxic load between 1994 and 2016 skyrocketed with the expanding vaccination schedule, acetaminophen use, the GMO revolution, etc.,” Hooker said.
Hooker argues that while evolving diagnostic criteria may explain part of the increase in autism and ADHD diagnoses, they are unlikely to account for the dramatic rise on their own.
Karl Jablonowski, Ph.D., Senior Research Scientist at Children’s Health Defense, also questioned the study’s narrow focus.
“The scores showed that genetic risk is not the primary driver of the autism epidemic explosion, something else is. And the authors, while ignoring absolutely every other contributor, conclude that that ‘something else’ must be over-diagnosis,” Jablonowski said.
These scientists point to a wide range of exposures that have expanded during the same period as autism prevalence, including pesticides, industrial chemicals, air pollution, heavy metals, endocrine-disrupting chemicals, wireless radiation, pharmaceuticals and other environmental toxicants.
Researchers continue to investigate how these exposures may interact with genetics during critical periods of brain development.
Genetics May Explain Susceptibility—Not Necessarily Cause
Autism has long been recognized as having a significant genetic component. However, many researchers distinguish between inherited susceptibility and factors that may trigger or influence whether neurodevelopmental conditions develop.
A growing body of research suggests that gene-environment interactions may be important. In these models, genetic susceptibility alone may not determine outcomes but instead influences how individuals respond to environmental exposures.
The Danish study’s finding that genetic risk scores have declined over time could therefore support multiple interpretations, not solely changes in diagnostic criteria.
Continuing the Search for Answers
The causes of autism and ADHD remain the subject of active scientific investigation.
While improved awareness and broader diagnostic practices have almost certainly contributed to increased identification, many researchers continue to examine whether environmental factors may also be influencing the rising prevalence of neurodevelopmental disorders.
As autism rates continue to increase worldwide, ethical scientists argue that understanding all potential contributors—including genetics, environmental exposures and their interactions—remains essential.
Studies that explore only one possible explanation may provide valuable insights, but they do not close the broader scientific debate about why autism and ADHD diagnoses continue to rise.
Sources:
LaBianca S, et al. Changes in Genetic Contributions to ASD and ADHD by Year of Diagnosis. JAMA Psychiatry.
Children’s Health Defense, The Defender. What’s Behind Skyrocketing Autism Rates — Better Diagnostics? Or an Avalanche of Toxins?
U.S. Centers for Disease Control and Prevention (CDC). Autism and Developmental Disabilities Monitoring (ADDM) Network.
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