19 February 2024

Early vocabulary size is genetically linked to ADHD, literacy, and cognition

Are genetic factors underlying children’s language development linked to later-life outcomes? In a genome-wide analysis, an international research team led by the Max Planck Institute for Psycholinguistics in Nijmegen found genetic associations between children’s early vocabulary size and later-life ADHD, literacy, and general cognition. These associations changed dynamically across the first three years of life. Both producing more words in infancy and understanding fewer words in toddlerhood were associated with a higher risk of ADHD.

Early language development is an important predictor of children’s later language, reading and learning skills. Moreover, language learning difficulties are related to neurodevelopmental conditions such as Attention-Deficit/Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD).

Children typically start to utter their first words between 10 and 15 months of age. At around two years of age, they may produce between 100 – 600 words, and understand many more. Each child embarks on its own developmental path of language learning, resulting in large individual differences. “Some variation in language development can be related to variation in the genetic code stored in our cells”, says senior researcher Beate St Pourcain, lead scientist on the study.

Word production and understanding

To understand how genetics plays a role in the development of children’s word production and understanding, the team carried out a genome-wide meta-analysis study (GWAS) of infant (15-18 months) and toddler (24-38 months) vocabulary size. In early measures of vocabulary size, parents report which words their children say and/or understand from a given word list.

The team used vocabulary and genetic data from 17,298 English-, Danish- or Dutch-speaking children. The number of spoken words was available for both infants and toddlers. The number of understood words was only available for toddlers. Later-life outcomes were mostly studied with genetic summary information from large independent consortia. These included literacy (spelling, reading, and phoneme awareness), cognition (general intelligence and number of years of education) and neurodevelopmental conditions (genetic risk of ADHD and ASD, as well as directly observed ADHD-related symptoms in some of the studied children).

“Learning to speak” and “Speaking to learn”

The researchers identified multiple genetic factors underlying vocabulary size in infancy and toddlerhood. Consistently, genetic associations with later-life literacy, cognition and ADHD-related measures varied during development. Both infant and toddler word production were related to literacy abilities such as spelling, but associations with general cognition were only found for toddler vocabulary scores. Toddlers have mastered some language fluency and may “speak to learn”, involving higher-level cognitive processing, while the development of verbal abiltities may start earlier.

The team also found that in infancy, a larger number of spoken words was genetically associated with both an increased risk for ADHD and more ADHD symptoms. However, this genetic relationship was reversed in toddlerhood: there, a smaller number of understood words was associated with more ADHD symptoms. It is possible that in infancy, when children are “learning to speak”, the number of spoken words captures speech-related processes. Also, children with a higher genetic risk of ADHD may be inclined to express themselves more. In contrast, during the phase of “speaking to learn” when vocabulary size is linked to cognition, higher genetic ADHD risk may be associated with lower verbal and cognitive abilities.

According to St Pourcain, “Genetic influences underlying vocabulary size rapidly change across less than two years during infancy and toddlerhood. Adopting a developmental perspective, our findings provide a better understanding of early speech- and language-related aetiological processes in health and disorder.” First author Ellen Verhoef adds: “This research indicates the relevance of vocabulary size assessed during the first few years in life for future behaviour and cognition, emphasising the need for more data collection efforts during infancy and toddlerhood.”

Link to paper

25 May 2022

Genetic study of childhood anxiety and depression

A genome-wide association study of childhood internalising symptoms by the EAGLE consortium was recently published in the Journal of the American Academy of Child and Adolescent Psychiatry (JAACAP). The study sheds light on the genetic architecture of early symptoms of depression and anxiety and reveals genetic overlap between childhood and adult mental health disorders. Christel Middeldorp, professor of Child & Youth Psychiatry at the University of Queensland said, “These findings are important because they help identify people most at risk of symptoms continuing across the lifespan, so intense treatment can be provided where needed.” Professor Middeldorp further highlights the results of this work in a press release published by the University of Queensland.

17 August 2021

Genomics of human aggression

The EAGLE “Genetic association study of childhood aggression across raters, instruments, and age” has now been accepted in Translational Psychiatry!
The study of “Continuity of Genetic Risk for Aggressive Behavior Across the Life-Course” has now been published in Behavior Genetics (doi: 10.1007/s10519-021-10076-6) and describes a successful application in Dutch and Australian cohorts of the PGS for aggression across the life span. Watch the space!