ADHD and autism traits share a common developmental spectrum

A large twin study suggests ADHD, autism, and related traits share a common neurodevelopmental spectrum linked to genetics and later learning outcomes.

Rethinking neurodevelopmental conditions: The need for a dimensional approach

Neurodevelopmental difficulties, such as issues with attention, communication, learning, cognition, movement, and language, are common, often inherited, and typically emerge early in life. Affecting about 15% of the global population, these conditions include ADHD, autism, learning and motor disabilities, and speech or language disorders.

Although categorized separately, they frequently overlap in symptoms and causes, and often co-occur with other psychiatric disorders. Focusing on a single diagnosis can miss or inadequately address co-occurring conditions, resulting in poorer outcomes. Research and clinical approaches must better identify and manage neurodevelopmental and co-occurring conditions to support the neurodivergent community.

Transdiagnostic psychiatric frameworks, such as the Hierarchical Taxonomy of Psychopathology (HiTOP), hierarchical causal taxonomies, and the Research Domain Criteria (RDoC), provide an alternative to traditional diagnostic systems by grouping symptoms across conditions based on shared characteristics. However, neurodevelopmental conditions are largely missing from these models, despite frequent co-occurrence with other psychiatric disorders. This gap is mainly due to most research focusing on adults, where neurodevelopmental traits are less common.

To address these gaps, researchers have proposed adding a “neurodevelopmental spectrum” to transdiagnostic psychiatric frameworks. This spectrum captures the shared features, developmental profiles, and etiological factors of neurodevelopmental conditions. Integrating neurodevelopmental traits with existing psychiatric spectra could advance understanding and management of neurodevelopmental conditions and their frequent comorbidities. However, major research gaps remain regarding the boundaries, causes, predictive value, and distinctiveness of this spectrum.

Examining the neurodevelopmental spectrum by analyzing traits, genetics, and outcomes

This study used longitudinal data from the Twins Early Development Study (TEDS) to investigate the composition, causes, predictive value, and specificity of the neurodevelopmental spectrum. Analyses modeled neurodevelopmental and psychiatric traits, examined twin and polygenic scores, and assessed cognitive and educational outcomes to clarify heritability, associations, and unique predictive utility.

TEDS is a nationally representative longitudinal study of over 16,000 twin pairs born in England or Wales between 1994–1996. Data were available at ages 7, 12, and 16, with sample sizes of 15,668, 12,465, and 10,261, respectively. Demographics matched the original cohort and the UK population at recruitment, including ethnicity and parental education/employment.

Neurodevelopmental and psychiatric traits, including ADHD, autism, learning and motor difficulties, internalizing and externalizing problems, were measured at ages 7, 12, and 16. Age-specific issues like psychotic and eating problems were assessed at age 16. Parents reported on traits at all ages, while self-reports were added at age 16.

Some participants also had genomic data at each age. Polygenic scores from recent GWAS were used: primary analyses focused on neurodevelopmental, cognitive, educational, and brain traits, while exploratory analyses included additional psychiatric and personality traits. Cognitive outcomes were general ability and reading skills at each age. Educational outcomes included teacher grades, exam scores, parent and teacher reports, and special education support.

Development, origins, and impact of neurodevelopmental difficulties across childhood and adolescence

The current study addressed four key questions to clarify the nature and impact of neurodevelopmental difficulties as children grow.

Structure and development of neurodevelopmental traits

Question one explored how neurodevelopmental traits evolve across childhood and adolescence. Parent reports revealed a hierarchical structure: a broad general (“p”) factor and several more specific factors that changed with age. Core neurodevelopmental difficulties, especially attention and learning problems, consistently emerged as a central factor from early childhood to adolescence.

As children matured, this broad factor gradually split into narrower domains, such as inattention, hyperactivity, and learning difficulties. For example, at age 7, the factor encompassed attention issues, low prosocial behavior, and learning problems, but by ages 12 and 16, it further separated into distinct components, such as inattention, hyperactivity, and social rigidity.

Although ADHD and autistic traits consistently contributed to the neurodevelopmental spectrum across development, some autistic features, particularly social difficulties and restricted or repetitive behaviors, also showed partial overlap with other psychiatric dimensions.

Genetic and environmental origins

Question two examined what causes these neurodevelopmental traits. Twin studies showed strong genetic influences on the neurodevelopmental factor at all ages, with many genetic effects persisting as children grew. Polygenic scores for neurodevelopmental, cognitive, and educational traits predicted neurodevelopmental traits, especially in adolescence, explaining a small but significant portion of the variation. Unique (non-shared) environmental factors also contributed at each stage.

Early-life challenges, such as delayed language development, low birth weight, or early cognitive difficulties, were linked to more serious later neurodevelopmental problems, though these effects were generally modest.

Impact on cognitive and educational outcomes

Question three focused on outcomes. The neurodevelopmental factor significantly predicted lower cognitive ability and poorer educational achievement, both at the same age and in later years, although the effects were small to moderate.

Genetic analyses showed overlapping genetic influences between neurodevelopmental difficulties and cognitive/educational outcomes. Children with more neurodevelopmental difficulties were genetically more likely to require special education and have lower cognitive ability.

Specificity of neurodevelopmental associations

Question four assessed whether these associations were unique to neurodevelopmental traits. Even after accounting for other psychiatric factors, the neurodevelopmental factor remained specifically linked to early-life predictors and later cognitive and educational outcomes, underscoring its distinct and meaningful role.

Transdiagnostic insights for improved outcomes

A rigorously characterized, genetically sensitive longitudinal sample provided new insights into the neurodevelopmental spectrum. The current study findings emphasize the importance of considering transdiagnostic dimensions to better understand neurodevelopmental conditions and their outcomes.

In the future, expanding transdiagnostic assessments and integrating the neurodevelopmental spectrum into dimensional classification systems will be crucial for enhancing research and clinical practice. This approach will support more comprehensive recognition of neurodevelopmental traits and associated psychiatric symptoms, with the long-term aim of informing more personalized and holistic assessment, support, and intervention strategies.

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Journal reference:

• Michelini, G. et al. (2026). The neurodevelopmental spectrum: Phenotypic architecture, etiology, predictive utility, and specificity across development. Molecular Psychiatry. 1-11. DOI: https://doi.org/10.1038/s41380-026-03714-0. https://www.nature.com/articles/s41380-026-03714-0