Autism & ADHD: The AuDHD Among Us

More Research Needed on the Autism and ADHD Overlap

Apr 01, 2024

Did you know that Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD) are comorbid, or often found together? Essentially, if you have either autism or ADHD, you probably want to get evaluated for the other just because they are so often co-occurring. Having both is often referred to as being AuDHD — the combination of autism and ADHD.

"Autism is the order to ADHD's chaos." —Dr. Devon Price in Unmasking Autism

You Can Have Both?

Yes. When The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (commonly referred to as the DSM-V) was published in 2013, autism and ADHD were finally recognized as potentially co-existing conditions.

Before that, both conditions were not able to be diagnosed together. In fact, ASD was an exclusion criteria for ADHD in the DSM-IV (the previous edition of the DSM). However, even before the DSM was updated in 2013, there were studies done that suggested a correlation between ASD and ADHD. I've listed a number of these studies later in this article.

What's the Difference Between ADD and ADHD?

Attention Deficit Disorder (ADD) is simply the old name for Attention Deficit Hyperactivity Disorder (ADHD). ADD was first added as a diagnosis in 1980 with the release of the DSM-III. The American Psychiatric Association (APA) changed the name to ADHD in 1987, and later added variations to the condition in the 1994 release of the DSM-IV: mostly hyperactive and impulsive, mostly inattentive, and a combined type that included all three symptoms.

Despite the many changes to the various editions of the DSM, some people still refer to ADHD as ADD, probably because they grew up using the latter term and are more familiar with it.

What Percentage of People Have Both ASD and ADHD?

That's the million-dollar question! The answer is that we're not entirely sure. Different studies have found a variety of percentages. There is a wide range of findings, although most of the evidence seems to point to a higher level of overlap than previously thought. Estimates range from around a 20 to 80 percent overlap in the diagnoses, which you can see evidence for in the next section.

Scientific Studies on the Comorbidity of Autism and ADHD

Interested in learning more about the overlap of autism and ADHD? Check out the following studies for more information, as well as the methodology and statistics used to come to those conclusions.

"Evidence indicates both disorders co-occur with a high frequency, in 20-50% of children with ADHD meeting criteria for ASD and in 30-80% of ASD children meeting criteria for ADHD" (Rommelse et al., 2010).
"According to the scientific literature, 50 to 70% of individuals with autism spectrum disorder (ASD) also present with comorbid attention deficit hyperactivity disorder (ADHD)" (Hours et al., 2022).
"This study aims to evaluate ADHD-like symptoms in children with autism spectrum disorder (ASD) based on single-item analysis, as well as the comparison of two ASD subsamples of children with ADHD (ASD+) and without ADHD (ASD-)... Of the sample, 53% [of children with ASD] fulfill DSM-IV criteria for ADHD" (Sinzig et al., 2009).
"The aims of this systematic chart review were to determine the frequency of attention-deficit/hyperactivity disorder (ADHD) in a clinic sample of children and adolescents with autism spectrum disorders (ASD)... Of 83 children, 78% fulfilled Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) criteria for ADHD and exceeded the 93rd percentile norm for the ADHD RS" (Lee & Ousley, 2006).
"Seventy percent of participants [children with ASD] had at least one comorbid disorder and 41% had two or more. The most common diagnoses were social anxiety disorder (29.2%, 95% confidence interval [CI)] 13.2-45.1), attention-deficit/hyperactivity disorder (28.2%, 95% CI 13.3-43.0), and oppositional defiant disorder (28.1%, 95% CI 13.9-42.2)" (Simonoff et al., 2008).

Why are ASD and ADHD Found Together?

That's another great question that we don't exactly have answers for yet. There are a number of theories as to why there is such an overlap between the two, but there is no concrete or definitive reason that scientists can find yet. Some theories include:

Genetics: Both ADHD and autism have a strong genetic component. More research is needed into how exactly genetics might play a role in this comorbidity.
Neurodevelopmental Reasons: Since both ASD and ADHD are neurodevelopmental disorders, it's thought that brain development was somehow affected, leading to an overlap in the disorders.
Brain Structure: We know that the structure of the autistic brain is different from the structure of a neurotypical brain, so it could be that simply having a different brain structure may make one more prone to having ADHD as well.
Environmental Factors: Some theorize that prenatal or perinatal exposure to neurotoxic compounds like pesticides, insecticides, and phthalate esters (often used in the production of electronic, packaging, and children's toys) could affect brain development, leading to ASD or ADHD or both. A study released in 2024 suggested that prenatal exposure to acetaminophen to adverse neurodevelopment in humans and animals, including higher rates of ADHD.

Conclusion: More Studies Needed

The overlap between Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD) is more common than many realize, with a significant percentage of individuals diagnosed with one disorder also showing symptoms of the other. While the exact reasons for this comorbidity remain unclear, research suggests a variety of potential contributing factors, including genetics, neurodevelopmental differences, and environmental influences. Understanding the co-occurrence of ASD and ADHD (AuDHD), is essential for improving diagnosis, treatment, and support for individuals who experience both.

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