Genetic Markers for ADHD Influence Toddler Activity Levels, Landmark Study of 80,000 Infants Reveals
Key Insights
An international study analyzing data from nearly 80,000 infants found that approximately 10% of variation in toddler activity levels can be explained by common genetic variants.
The genetic markers associated with early activity levels strongly overlap with those known to influence ADHD (search) risk later in childhood and adulthood.
Researchers identified the RHEBL1 (search) gene, where specific markers linked to lower toddler activity also appear to increase gene activity in the brain's cortex.
A toddler's activity levels are shaped in part by genetic differences, and many of the same genetic markers also influence the likelihood of developing Attention Deficit and Hyperactivity Disorder (ADHD (search)) later in life, according to groundbreaking research from the University of Surrey published in Nature Human Behaviour.
In the first study of its kind, an international team led by Professor Angelica Ronald, Professor of Psychology and Genetics at the University of Surrey, analyzed data from nearly 80,000 infants drawn from multiple national and international cohort studies to uncover the genetic architecture underlying early childhood activity levels.
"From 12 to 36 months is a very exciting time for parents and children, with a lot of new skills being learnt. During this time, we know that toddlers vary widely in how much they move around," said Professor Ronald. "We were interested to learn about the underlying biology of early activity levels and whether these behaviors share some of the same genetic influences that affect things late in life such as diagnoses of ADHD (search) and educational outcomes."
Genetic Overlap Between Toddler Behavior and ADHD
The researchers found that approximately 10% of the variation in toddler activity levels can be explained by common genetic differences identified in the study. Critically, the genetic markers they discovered were found to overlap strongly with those that influence the likelihood of ADHD (search), which is typically diagnosed later in childhood or in adulthood.
"We did not know until now that the genetic basis of ADHD (search) was shared with these early behavioral traits," said Anja Hollowell, first author of the study, who completed the work while at the University of Surrey and Birkbeck and is now based at University College London. "Our findings show that very early activity levels are influenced by many of the same genetic markers that influence later ADHD. Earlier identification of ADHD would be very helpful for providing timely support to children and their families."
The Role of RHEBL1 and Brain Development
As a specific example, the team identified markers in the gene RHEBL1 (search) that were associated with lower toddler activity levels. These same genetic markers also appear to affect how active the RHEBL1 gene is in the cortex, a major region of the brain. In other words, the DNA variations that seem to influence lower toddler activity levels also appear to upregulate the activity of the RHEBL1 gene in this brain region.
This finding opens new avenues for understanding how a child's early activity levels are shaped by their biology and could help scientists better understand the relationship between movement, brain development, and learning.
Broader Behavioral Traits and Lifespan Connections
Beyond activity levels, the study also identified genetic variants associated with other key toddler behaviors, including sociability, emotionality, and shyness. Multiple genes were found to be associated with these traits.
Notably, the genetic markers associated with toddler emotionality were also linked to neurotic personality traits in adulthood. Furthermore, the genetic variation associated with toddler emotionality and low sociability overlapped with genetic variation known to be associated with the likelihood of autism.
"For the first time, we have identified the genetic variation associated with these early behavioral traits in toddlers. Our work highlights the significance of 'nature' in a young child's behavior," Professor Ronald said. "This complements the existing research on environmental influences on early childhood. These new results advance our understanding of the early pathways influencing individual differences in child development."
Implications for Early Intervention
The findings carry significant implications for clinical practice and early childhood development. Professor Ronald noted that the results "can be used to think about how better to identify young children who would benefit from early interventions for their ADHD (search)-like behaviors." By understanding the genetic underpinnings of early activity patterns, clinicians and families may eventually have tools to recognize children at elevated risk and provide timely support before formal diagnosis becomes possible.