How Similar Are Autism, ADHD, and OCD in Brain Structure and Behavior?

What you need to know

• The study found significant overlap in brain structure and behavior across autism, ADHD, and OCD, challenging the idea that these are distinct disorders.
• Data-driven analysis identified groups of individuals with similar brain and behavior characteristics that did not align well with traditional diagnostic categories.
• The results suggest autism-like features and inattention may exist along a continuum that includes typical development, rather than as discrete categories.

Background and purpose of the study

Autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), and obsessive-compulsive disorder (OCD) are complex neurodevelopmental conditions that are currently treated as distinct disorders. However, growing evidence suggests there may be significant overlap between these conditions in terms of genetics, brain structure and function, and behavioral symptoms.

This study aimed to take an unbiased look at whether individuals naturally group together based on their brain structure and core behavioral traits in ways that match up with current diagnostic labels, or if different groupings emerge. The researchers used advanced computational techniques to analyze brain imaging and behavioral data from children and adolescents with ASD, ADHD, OCD, and typical development.

How the study was conducted

The study included 226 participants aged 6-18:

• 112 with ASD
• 58 with ADHD
• 34 with OCD
• 22 typically developing controls

The researchers collected two main types of data:

1. Brain structure: They used MRI brain scans to measure the thickness of the cerebral cortex (the outer layer of the brain) in 76 regions.

2. Core behavioral traits: They used questionnaires to assess three key areas of difficulty associated with ASD, ADHD and OCD:

   • Social communication difficulties (associated with ASD)
   • Inattention (associated with ADHD)
   • Obsessive-compulsive traits (associated with OCD)

Rather than comparing pre-defined diagnostic groups, they used a data-driven approach called “bagged multiview clustering.” This technique grouped participants based on similarities in their brain structure and behavioral traits, without considering their diagnosis. The researchers then examined how well these data-driven groups matched up with the original diagnostic categories.

Key findings

Overlap between disorders

The study found significant overlap between ASD, ADHD and OCD in both brain structure and behavioral traits:

• Many participants showed elevated scores on questionnaires assessing traits typically associated with other disorders. For example, 46% of those with ASD met the cutoff for clinically significant ADHD symptoms.

• When plotted on a graph, the distribution of scores for social communication difficulties and inattention showed substantial overlap between diagnostic groups.

Data-driven groupings vs diagnostic categories

The groups identified by the data-driven analysis did not align well with traditional diagnostic categories:

• Most of the data-driven groups contained a mix of participants from different diagnostic categories.

• Statistical measures showed low agreement between the data-driven groups and original diagnoses.

• Only one small group emerged that contained only participants with ASD (12% of the ASD sample).

Continuum of traits

The results suggested that autism-like features and inattention may exist along a continuum that includes typical development, rather than as discrete categories:

• When participants were plotted based on their scores for social communication difficulties and inattention, they formed a continuous distribution rather than distinct clusters.

• The data-driven groups appeared to divide this space into regions of low and high inattention, with a range of social communication difficulties within each region.

Brain regions involved

The brain regions that contributed most to determining the data-driven groups were involved in:

• Social functioning
• Emotion processing
• Language
• Attention
• Inhibitory control

Many of these regions have been implicated in previous brain imaging studies of ASD, ADHD and OCD. However, no single region or small set of regions drove the groupings. Instead, subtle differences across many brain areas appeared to be important.

Conclusions

• The study findings challenge the validity of ASD, ADHD and OCD as distinct disorders with unique underlying biology and symptoms.

• There appears to be significant overlap between these conditions, with traits like social difficulties and inattention potentially existing along a continuum that includes typical development.

• Data-driven approaches that look at patterns of brain structure and behavior, rather than starting with diagnostic labels, may provide new insights into neurodevelopmental differences.

• Future research and clinical practice may need to move beyond traditional diagnostic categories to better capture the complex variation in brain development and behavior.

While this single study cannot definitively overturn existing diagnostic categories, it adds to growing evidence that our current classification system may not optimally reflect the underlying neurobiology of these conditions. Larger studies examining multiple aspects of brain structure and function, genetics, and behavior across development are needed to further clarify these issues.