There may be a link between white matter in the brain and autism.
Researchers at the New York University (NYU) School of Medicine have found a consistent connection between structural abnormalities in the brain’s white matter with the severity of symptoms in people with autism.
The study was published earlier this month in JAMA Psychiatry.
Researchers say these findings hold true in children with autism spectrum disorder (ASD) as well as, to some degree, in children with attention deficit hyperactivity disorder (ADHD) who have autistic traits.
According to the Centers for Disease Control and Prevention (CDC), one in 68 children has some degree of ASD.
The American Psychiatric Association estimates that 1 in 20 children have ADHD.
The dimensional approach
The study adds to the understanding of what the brain’s makeup can tell us about ASD and ADHD.
While the researchers hope to provide clinicians and researchers with further insights, the senior author of the study cautions that there’s still work to be done in understanding these tricky conditions.
“It’s been quite recently accepted that many kids with an autism diagnosis may have behavioral symptoms similar to ADHD,” Dr. Adriana Di Martino, the study’s senior author and an associate professor in the Department of Child and Adolescent Psychiatry at NYU School of Medicine, told Healthline.
“It’s less recognized, and it’s only starting to emerge now, that children with ADHD may have qualitative impairments similar to autism,” she added. “There’s been a movement initiated by the National Institute of Mental Health (NIMH) stressing the importance of dimensional approaches. It’s called the RDoC, the Research Domain Criteria, which emphasizes the importance of looking at dimensions, whether they’re psychopathological markers or symptoms or cognitive traits, that track across diagnoses.”
Simply put, this dimensional approach places a strong emphasis on understanding the shades of gray, rather than the black and white, of a diagnosis.
RDoC looks at the degree to which a person shows traits, and seeks to understand how related psychological characteristics present themselves in people with these conditions.
Researchers in the NYU study examined white matter nerve bundles in the brain, finding a strong link between structural issues in the white matter and symptom severity.
This was most apparent in the corpus callosum, the region that connects and enables communication between the left and right cerebral hemispheres of the brain.
In all, the brains of 174 children were examined. Of them, 69 had a diagnosis of ASD, 55 had an ADHD diagnosis, and 50 were developing typically.
A complex puzzle
Both ASD and ADHD are notoriously difficult for clinicians, researchers, and parents to fully understand because different people exhibit different traits.
To that end, Di Martino and her team at NYU hope to build on their findings so these connections can be more thoroughly understood.
“From a clinical perspective, it would be very helpful to better inform clinicians,” she said. “The term ‘autistic traits’ encompasses numerous areas of impairment. It could entail specific social language impairments, or social reciprocity difficulties, or even sensory processing abnormalities. What we have been able to do so far is look at the overall picture, but we don’t know which of these aspects are driving these relationships.”
The research suggests that there are shared disease mechanisms across ASD and ADHD diagnoses, creating the possibility of better and more accurate diagnostic tests in the future.
But more research is needed.
Di Martino say it’s important that future studies have a deep phenotyping of large samples with multiple diagnoses to help build a better understanding.
“This would help clinicians when they are evaluating a child who comes in with concerns about one or the other disorder to figure out what comes first,” she said. “Trying to dissect what aspects are driving these impairments would be helpful.”
Researchers also continue to see value in the dimensional approach to clinical diagnosis, but this is just part of the picture.
“We’re looking at the severity, the symptoms, the continuum, and the degree of the severity,” said Di Martino. “But it’s hard to assume that it’s just about dimensions. The RDoC is encouraging researchers and clinicians alike to think in a diagnostic way, and this is really important. It has implications for the clinical approaches, and it has implications for future discoveries.”
While the NYU researchers have uncovered some intriguing possibilities, Di Martino noted that the study has not been confirmed, that there are common developmental pathways between the two disorders.
“When I talk about kids with ADHD who have qualitative impairments similar to those observed in autism, I’m still talking about 20 to 30 percent of the kids with ADHD,” she explained. “It’s important to know this because many kids with ADHD may have social difficulties. In fact, 70 to 80 percent are known to have social difficulties. But not all social difficulties observed in kids with ADHD are qualitatively similar to those observed in kids with autism. But that 20 to 30 percent may need to be recognized, observed, and treated differently. We don’t know yet. But this type of effort, and the questions we’re asking, will hopefully get others asking those questions as well.”