Marina Sarris

Date Published: September 29, 2026

Youngsters Marley and Carter sometimes struggle with learning and managing behavior. Is this because they have autism? Or is it because they sleep poorly? Or is it their learning disabilities?

“It’s hard to separate what’s coming from autism and what’s coming from something else. They kind of blend together,” says their mother, Laura Youker, of California.

Her 7-year-old and 5-year-old are among many people who have other conditions that may, at times, seem to overlap with their autism.

Autistic people are more likely than the general population to have attention-deficit/hyperactivity disorder (ADHD), learning disabilities, anxiety, depression, intellectual disability, bipolar disorder, epilepsy, sleep disorders, and gastrointestinal problems, according to research studies. These are called “co-occurring conditions” to autism.

“It’s important to know what conditions individuals with autism are at higher risk for,” explains researcher Magdalena Janecka, Ph.D., associate professor at NYU Langone Health. This information could help families recognize, and doctors screen for, co-occurring conditions if symptoms arise, she says. And understanding these other conditions could shed light on the origins of autism, she adds. What links them together?

How do you draw a line between autism and other conditions?

Years ago, certain conditions seemed so common in autistic people that some doctors assumed they were part of autism.^1,2  Until 2013, in fact, the psychiatric diagnostic manual discouraged doctors from diagnosing ADHD in autistic people. Many doctors ignored that warning, believing that it was better to diagnose and treat ADHD symptoms in autistic patients who had them.

Today, ADHD is one of the most commonly diagnosed co-occurring conditions in children and adults with autism, according to research.^3,4

One team of researchers examined the different diagnoses of 40,500 autistic children, along with their siblings who don’t have autism.³ The children were all participants in the SPARK autism study. Siblings form a good comparison group because they share similar genes and environments, both of which can play a role in health conditions, explains Janecka, who was part of that research team.

The team found that 35 percent of the autistic children have ADHD, compared with just 17 percent of their siblings without autism.³

Almost 75 percent of the autistic children were diagnosed with at least one other medical condition, including sleep disorders, mood disorders, motor delays, and seizures. By comparison, about 30 percent of their siblings had a diagnosis on the list.

Learning disability (24 percent) and intellectual disability (22 percent) were the second and third most common conditions in autistic children in SPARK.

About 19 percent of the children had anxiety. The rate is higher in autistic adults in SPARK. One third of adults with a guardian, and two-thirds of independent adults, reported an anxiety disorder. Similarly, autistic adults in SPARK also report a higher rate of ADHD diagnoses than the children.⁵

Other studies have found similar results. Autistic people have higher rates of mental health conditions than the general population, according to an analysis of 96 studies that was conducted by researchers in Canada and the United Kingdom.⁴

Why are autistic people more likely to have certain other conditions?

What might be causing this clustering of other medical conditions in many autistic people? The answer may be found in their DNA and environmental influences.

Some of the rare variations in genes that contribute to autism affect different parts of the body, such as the gastrointestinal tract and the brain. Scientists also have found a link between several conditions and certain environmental exposures during pregnancy, birth, and infancy.

In the study of SPARK children and their siblings, Janecka’s research team analyzed  the pregnancy and birth complications reported by their parents. The team focused on children who joined SPARK before age 18 because their parents’ memories of early complications would be fresher. The team examined complications, such as serious prenatal infections, premature birth, loss of oxygen at birth, and brain bleeds during delivery, among others.

As a group, parents reported more of these complications with their autistic children than their children who did not have autism. Children exposed to such problems were more likely to have ADHD, motor delays, or other conditions than children with no complications, whether they had autism or not.³

But that does not mean the complications caused these other conditions to occur. “We’re very far from cause and effect here,” cautions Janecka.

Her research team found a link between premature or preterm birth and motor delays in autistic children. “We know that there are a lot of shared risk factors for both conditions,” she explains. “So there could be, for example, certain genetic factors that cause preterm birth and also cause motor delays. We can’t establish that preterm birth causes motor delay because we didn’t look at those genetic factors that could exist.”

Future research may uncover why certain conditions are more common in autistic people, and how genetic and environmental factors play a role, she says.

She is currently studying the genetic risks for prenatal and birth complications among participants in SPARK. Her team wants to know: “Are autistic individuals genetically more likely to be born preterm, for example, compared with their unaffected siblings?” If the answer turns out to be yes, it could mean that certain genetic factors may increase the likelihood of both premature birth and autism, she explains.

Is this autism, or something else?

Doctors understand that the boundaries between different mental health conditions, not just autism, can be blurry. That means that “many symptoms assigned to a single disorder may occur, at varying levels of severity, in many other disorders,” according to the current psychiatric diagnostic manual.⁶

For example, behaviors repeated over and over again – such as lining up objects and having a rigid routine – could be part of an “insistence on sameness” in autism or a compulsion in obsessive-compulsive disorder.

Doctors should use their training and experience to sort it all out, the manual suggests.

“It is important to distinguish certain symptoms that are part of autism versus symptoms of another condition,” says Janecka, the researcher. “I think we can’t always easily tell.” That’s partly because autism can look very different in people who have it, she says.

One trait of autism, social communication differences, can also complicate diagnosis. For example, some autistic people find it hard to recognize and describe their symptoms to a doctor. That’s especially true if they have limited or no speech.

Laura Youker said that her daughter, who is nonspeaking, began to act differently at school. Marley cried and didn’t listen to her teacher. Those episodes could have been mistaken for problems with attention or managing emotions, which are fairly common in autistic children.

But fortunately, the real cause was found and treated. Marley had a tooth infection. “So, once those teeth were fixed, she was perfectly fine,” says Youker, a member of the SPARK Community Advisory Council.

Getting a diagnosis, whether for a dental infection, sleep disorder, learning disability, or anxiety, can make it easier to get the right treatment and support.

That was the case for Trudi Sullivan, an autistic adviser to SPARK. When she was in her 20s, she was diagnosed with a learning disability, auditory perceptual disorder, and received help for it. Then, in her 50s, she was diagnosed with autism and anxiety. She learned more about each condition and found the right care. “There’s help out there if you seek it,” she says.

Interested in joining SPARK? Here’s what you should know.

Photo by iStock.

References

1. American Psychiatric Association. Diagnostic and statistical manual of mental disorders (4th ed., rev.). Washington, DC: APA (2000)
2. Leyfer O.T. et al. J. Autism Dev. Disord. 36, 849-861 (2006) PubMed
3. Khachadourian V. et al. Transl. Psychiatry 13, 71 (2023) PubMed
4. Lai M.C. et al. Lancet Psychiatry 6, 819-829 (2019) PubMed
5. SPARK Snapshot Dec. 2015 – Dec. 2025. Accessed Sept. 14, 2026
6. American Psychiatric Association. Diagnostic and statistical manual of mental disorders (5th ed.) Arlington, VA: APA (2013)