How Genes Steer the Path Toward Autism or ADHD
Author: Professor Anders Børglum, Aarhus University, Department of Biomedicine.
Published: 4 Oct 2022 - Updated: 19 Jul 2026
Publication Details: Peer-Reviewed | Research, Study, Analysis
Table of Contents:
Synopsis - Definition - Overview - FAQs - Insights, Updates - Related Content
Synopsis
This research, a peer-reviewed genome-wide association study led by Professor Anders Børglum of Aarhus University and Denmark's iPSYCH project, examines why autism and ADHD so often overlap yet remain distinct conditions. Analyzing 8.9 million genetic variants across the genomes of 34,462 people diagnosed with autism spectrum disorder and/or ADHD alongside 41,201 controls, the team pinpointed seven genetic variants common to both disorders and five variants specific to just one. A striking finding is that some variants raising autism risk also boost cognitive function and alter the volume of a specific brain area, while their complementary ADHD-linked variants tend to lower cognition and shift that brain region in the opposite direction. The work matters for autistic people, those with ADHD, their families, clinicians, and researchers because it offers the first clear evidence that individuals with both diagnoses carry a double genetic burden, lending biological support to revised guidelines such as the DSM-5 that now allow both conditions to be diagnosed in the same person and pointing toward earlier, more precise diagnosis and treatment.*
At a Glance
- 1 - An autism diagnosis is typically made before an ADHD diagnosis. Hyperactivity and concentration difficulties can be masked by autism symptoms, so the ADHD challenges may go unnoticed.
- 2 - Until recently, an official diagnosis hierarchy made it impossible in principle to diagnose ADHD in a person who already had autism. This study offers a biological argument against that older approach.
- 3 - The findings drew on multiple analytic layers, including a Brain Transcriptome-Wide Association Study that links variants to gene expression in specific brain regions and cell types. Results were also compared against genetic studies of other mental disorders and traits.
Topic Definition
- Autism and ADHD Genetics
Autism And ADHD Genetics refers to the study of the inherited variations in DNA that influence whether a person develops autism spectrum disorder, attention deficit hyperactivity disorder, or both. Both conditions are among the most common neurodevelopmental diagnoses in childhood, both run strongly in families, and both share a substantial portion of their underlying genetic causes, which helps explain why they so frequently occur together in the same individual. Researchers use large-scale methods, such as genome-wide association studies, to compare millions of genetic markers across tens of thousands of people, searching for the specific variants that raise risk. What makes this field especially interesting is that some variants appear to be shared between the two disorders while others tip development toward one diagnosis over the other, and certain variants even affect broader traits like cognitive ability and the size of particular brain regions. Understanding this genetic architecture is helping scientists separate what these conditions have in common from what sets them apart, with the long-term aim of earlier, more accurate diagnosis and more personalized care.
Overview
There is a large overlap between the genetic causes of autism and ADHD. Now, researchers from Aarhus University have found gene variants that increase the risk of developing only one of the diagnoses and not the other.
In the group of neurodevelopmental disorders, ADHD and autism have several things in common: They are two of the most common child psychiatric diagnoses, both diagnoses are highly heritable, and although they differ from each other in the core symptoms, autism and ADHD have a significant overlap in their underlying genetic causes.
Researchers have identified seven genetic variants common to autism and ADHD and five gene variants specific to only one of the two diagnoses.
"We have succeeded in identifying both shared genetic risk variants and genetic variants that differentiate the two developmental disorders," says Professor Anders Børglum of the Department of Biomedicine at Aarhus University and iPSYCH, Denmark's largest research project within psychiatry, which is behind the study.
"That means that we are beginning to understand both the biological processes that are behind the development of both diagnoses and - as something completely new - also the processes that push the developmental disorder specifically in the direction of either autism or ADHD."
What Happens in the Brain?
The genetic variants affect brain nerve cells and how the brain develops and communicates. It is also remarkable that some genetic variants impact people's cognitive functions.
Specifically, the researchers can, for example, see that some of the genetic variants that only increase the risk of autism also increase the cognitive functions of individuals, while the complementary variants, which only increase the risk of ADHD, generally reduce the cognitive functions of individuals.
Similarly, the researchers have identified a gene variant that increases the risk of autism and, simultaneously, reduces the volume of a specific brain area in people in the general population. In contrast, the complementary variant increases the risk of ADHD and increases the volume of this brain area.
Altered Diagnostic Guidelines
It may seem obvious, but the study is the first in the world to show that people with both ADHD and autism are double-burdened with a genetic risk of receiving both diagnoses, whereas people who only have one of the diagnoses for the most part only bear the genetic risk variants for this one condition.
"This means, for example, that people with both diagnoses have an equally large load of ADHD genetic factors as people who only have ADHD, and at the same time, the same large load of autism genetic factors as people who only have autism. So it makes perfect biological sense that some people have both diagnoses," says Anders Børglum.
The researchers analyze large datasets of genetic profiles to learn more about diseases and developmental disorders. This can make it possible to create more precise diagnoses and earlier interventions and ensure that the individual patient receives the right treatment.
"The autism diagnosis is typically made before an ADHD diagnosis. So if, for example, the person is also hyperactive and finds it difficult to concentrate, this may well be slightly drowned out by the autism symptoms, and we may not see the ADHD challenges," explains Anders Børglum.
"But if we have a genetic study of a person with an autism diagnosis, and we see a major genetic load of ADHD genetics, then it may be that we should monitor that person a bit more closely. In this way, we can become quicker to spot the development and give the family good tools to handle this diagnosis, too."
A few years ago - due to an official diagnosis hierarchy - it was not in principle possible to diagnose ADHD in a person who had autism, he says.
"But now we have shown that people with both diagnoses are in fact double burdened with the genetic risk of both developmental disorders. There is thus a clear biological difference between whether you have both diagnoses or just one. The study is, therefore, a strong biological argument for the revised diagnostic guidelines, e.g., in the American Diagnosis and Classification system for Mental Disorders (DSM-5), where it is now possible for the same person to receive both diagnoses," says Anders Børglum.
"This is the first step. Here and now, the study is relevant because it helps better to understand the causes of the two developmental disorders. In the long term, this can form the basis for better diagnostics and treatment."
Behind the Research Results
The study examines genetic variations in the genomes of 34,462 people diagnosed with Autism Spectrum Disorder and/or ADHD, and 41,201 control subjects without these diagnoses (a so-called GWAS, genome-wide association study). 8.9 million genetic variants have been examined for each person, spread across the entire genome.
By correlating the genetic results with data from the genes' expression in different regions of the brain and brain cells, e.g., in a so-called Brain Transcriptome-Wide Association Study (TWAS), the researchers can examine the consequences of various genetic risk variants.
The researchers obtain more information about the significance of the genetic risk variants by comparing the results of the autism/ADHD analyses with the results of genetic studies of other mental disorders and general traits, such as cognitive functions and the volume of brain regions.
About the Study
The study is headed by the Danish iPSYCH researchers with many international partners, including the Psychiatric Genomics Consortium (PGC) and the Broad Institute of MIT and Harvard. iPSYCH is primarily financed by the Lundbeck Foundation.
Frequently Asked Questions
NOTE: Researched FAQs by Disabled World (DW)
Can a person be diagnosed with both autism and ADHD at the same time?
Yes, current diagnostic guidelines such as the DSM-5 allow a person to receive both diagnoses simultaneously. Research shows that individuals with both conditions carry the genetic risk factors for each, which supports diagnosing them together.
Are autism and ADHD inherited from parents?
Both conditions are highly heritable, meaning genetics play a large role in whether they develop. However, inheritance is complex and involves many gene variants, so having a family member with either condition raises but does not guarantee risk.
Does having a genetic risk variant mean a person will definitely develop autism or ADHD?
No, carrying a risk variant increases the likelihood but does not make either condition certain. These disorders arise from the combined effect of many genes and other factors, so risk is a matter of probability rather than destiny.
Can genetic testing currently diagnose autism or ADHD?
Genetic testing is not yet used to diagnose either condition on its own, since diagnosis relies on behavioral and developmental assessment. Research like this may eventually help refine diagnostics, but clinical evaluation remains the standard.
Why do autism and ADHD symptoms sometimes look similar?
The two conditions share overlapping genetic causes that affect how the brain develops and communicates, which can produce related challenges with attention, social interaction, and behavior. This biological overlap partly explains why their symptoms can resemble one another.
Do these genetic findings apply equally to adults and children?
The study focused on genetic risk that is present from birth and shapes lifelong brain development, so the biology applies across ages. That said, both conditions are most often first diagnosed in childhood, and symptoms can change over a person's lifetime.
Could this research lead to new treatments for autism or ADHD?
In the long term, understanding the specific genes and brain processes involved could guide the development of more targeted therapies. For now, the findings mainly improve understanding of the causes rather than offering new treatments directly.
Insights, Analysis, and Developments
Editorial Note: The scale and collaboration behind this work are worth noting, drawing on international partners including the Psychiatric Genomics Consortium and the Broad Institute of MIT and Harvard, with iPSYCH funding largely provided by the Lundbeck Foundation. For families navigating a child's overlapping symptoms, the practical takeaway is quietly significant: a genetic profile showing a heavy ADHD load in someone already diagnosed with autism could prompt closer monitoring and earlier support, catching difficulties that might otherwise slip past. What the researchers describe as a first step is really a shift in how these conditions are understood, moving from behavior alone toward the underlying biology, and that shift carries real promise for sharper diagnosis and better-matched treatment in the years ahead.*
Attribution/Source(s): This peer reviewed publication was selected for publishing by the editors of Disabled World (DW) due to its relevance to the disability community. Originally authored by Professor Anders Børglum, Aarhus University, Department of Biomedicine. and published on 4 Oct 2022, this content may have been edited for style, clarity, or brevity.
* Editorial additions by Ian C. Langtree.