Genetic differences affecting infant's activity also associated with ADHD, study finds Jul 2 Genetic differences or variations in DNA sequences that affect a toddler's activity levels could also be associated with ADHD, a new study has found. Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental condition characterised by short attention spans and impulsive, restless behaviour.

"We did not know until now that the genetic basis of ADHD was shared with these early behavioural traits (activity levels displayed as a toddler)," first author Anja Hollowell, from the universities of Surrey and Birkbeck in the UK, said.

"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," Hollowell said.

Angelica Ronald, lead author of the study published in the journal Nature Human Behaviour and professor of psychology and genetics at the University of Surrey, said, "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." "Activity levels are important and likely influence a wide variety of experiences including learning, exploring the wider environment, development of motor skills and the type of parenting that children receive," Ronald said.

An international team of scientists analysed data from nearly 80,000 infants from multiple national and international cohort studies, including British and European, to discover the genetic differences that influence toddler activity levels.

Ten per cent of the variation in activity levels between toddlers could be explained by common genetic differences discovered by the researchers.

The genetic markers or indicators the team discovered were found to overlap strongly with those that influence likelihood of ADHD, which is diagnosed later in childhood or in adulthood.

For example, markers in the gene 'RHEBL1' were identified as being associated with lower toddler activity levels.

The same genetic markers also affect how active the RHEBL1 gene is in the cortex, a major region of the brain, the researchers said.

In other words, the same DNA variations that seem to influence lower toddler activity levels also appear to turn up the activity of the RHEBL1 gene in the brain's cortex region, they said.

The findings open up new avenues for understanding how a child's early activity levels are shaped by biology and could help scientists better understand the relationship between movement, brain development and learning, the team said.

Ronald added, "For the first time, we have identified the genetic variation associated with these early behavioural traits in toddlers. Our work highlights the significance of 'nature' in a young child's behaviour." "This (study) 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," the lead author said.

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