Genetic Links Between Vocabulary and Later-Life ADHD Shift Over Infancy and Toddlerhood
A larger span of spoken words was genetically linked with an increased risk of attention-deficit/hyperactivity disorder (ADHD) and more ADHD symptoms in infants. But by toddlerhood the genetic relationship was reversed, and a smaller number of understood words was associated with more ADHD symptoms. Researchers published findings from their meta–genome-wide association study in Biological Psychiatry.
“These findings implicate dynamic and rapid changes in the genetic architecture of vocabulary acquisition across a period of less than 2 years,” wrote senior researcher and corresponding author Beate St. Pourcain, PhD, of the Max Planck Institute for Psycholinguistics in the Netherlands and study coauthors. “Specifically, they underline the importance of adopting a developmental perspective when studying the biology underlying early-life vocabulary development and shared links with neurodevelopmental conditions.”
The study included 37,913 parent-reported vocabulary size measures for 17,298 English-, Danish-, or Dutch-speaking children of European descent. Parent reports on the number of spoken words were available for both infants (15-18 months) and toddlers (24-38 months), while the number of understood words was available only for toddlers. Later-life outcomes including literacy, cognition, and ADHD symptoms were investigated using genetic summary information from large independent consortia.
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According to the study, numerous genetic factors underlied vocabulary size in infants and toddlers. Genetic links with later-life literacy, cognition, and ADHD symptoms consistently varied over development. For example, literacy skills such as spelling were related to word production in both infanthood and toddlerhood, although general cognition was only associated with toddler vocabulary. Later-life ADHD symptoms, meanwhile, were genetically associated with more spoken words during infancy and with fewer understood words during toddlerhood.
The research team theorized that the number of spoken words in infancy may reflect speech-rated processes, and that infants with a higher genetic risk for ADHD may be prone to express themselves more. In contrast, higher genetic ADHD risk may be associated with lower verbal and cognitive abilities in toddlerhood, when vocabulary size is associated with cognition.
“This research indicates the relevance of vocabulary size assessed during the first few years in life for future behavior and cognition, emphasizing the need for more data collection efforts during infancy and toddlerhood,” said first and corresponding author Ellen Verhoef, PhD, of the Max Planck Institute for Psycholinguistics.
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