Early Words Shape Future Brain: Genetic Link Between ADHD and Language

Summary: A new study delves into the genetic underpinnings of language development in early childhood and its implications for later cognitive abilities and neurodevelopmental disorders like ADHD and ASD.

By analyzing vocabulary data from over 17,000 children across different languages, the study uncovers how genetics influences word production and comprehension from infancy to toddlerhood, revealing that vocabulary size is not only a marker of early language skills but also predictive of future literacy, cognition, and potential neurodevelopmental challenges.

Interestingly, the research highlights a developmental shift in the genetic associations with ADHD symptoms, suggesting that the role of genetics in language development and its impact on neurodevelopmental outcomes is complex and changes over time. This study underscores the importance of understanding the early linguistic journey as a window into a child’s future mental health and cognitive prowess.

Key Facts:

  1. Genetic Basis of Language Development: The study identifies genetic factors that influence vocabulary size in early childhood, linking these genetic influences to later literacy, cognition, and ADHD symptoms.
  2. Shift in Genetic Associations with ADHD: Initially, a larger vocabulary in infancy is associated with a higher risk for ADHD, but this relationship reverses in toddlerhood, suggesting a nuanced role of genetics in language development and neurodevelopmental outcomes.
  3. Educational and Therapeutic Implications: These findings emphasize the need for early interventions tailored to children’s genetic predispositions, potentially aiding in the prevention or mitigation of cognitive and neurodevelopmental issues.

Source: Max Planck Institute

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.

This shows a young girl and a brain.
The researchers identified multiple genetic factors underlying vocabulary size in infancy and toddlerhood. Credit: Neuroscience News

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.”

About this genetics, ADHD, and language research news

Author: Marjolein Scherphuis
Source: Max Planck Institute
Contact: Marjolein Scherphuis – Max Planck Institute
Image: The image is credited to Neuroscience News

Original Research: Open access.
Genome-wide Analyses of Vocabulary Size in Infancy and Toddlerhood: Associations With Attention-Deficit/Hyperactivity Disorder, Literacy, and Cognition-Related Traits” by Beate StPourcain et al. Biological Psychiatry


Genome-wide Analyses of Vocabulary Size in Infancy and Toddlerhood: Associations With Attention-Deficit/Hyperactivity Disorder, Literacy, and Cognition-Related Traits


The number of words children produce (expressive vocabulary) and understand (receptive vocabulary) changes rapidly during early development, partially due to genetic factors. Here, we performed a meta–genome-wide association study of vocabulary acquisition and investigated polygenic overlap with literacy, cognition, developmental phenotypes, and neurodevelopmental conditions, including attention-deficit/hyperactivity disorder (ADHD).


We studied 37,913 parent-reported vocabulary size measures (English, Dutch, Danish) for 17,298 children of European descent. Meta-analyses were performed for early-phase expressive (infancy, 15–18 months), late-phase expressive (toddlerhood, 24–38 months), and late-phase receptive (toddlerhood, 24–38 months) vocabulary. Subsequently, we estimated single nucleotide polymorphism–based heritability (SNP-h2) and genetic correlations (rg) and modeled underlying factor structures with multivariate models.


Early-life vocabulary size was modestly heritable (SNP-h2 = 0.08–0.24). Genetic overlap between infant expressive and toddler receptive vocabulary was negligible (rg = 0.07), although each measure was moderately related to toddler expressive vocabulary (rg = 0.69 and rg = 0.67, respectively), suggesting a multifactorial genetic architecture. Both infant and toddler expressive vocabulary were genetically linked to literacy (e.g., spelling: rg = 0.58 and rg = 0.79, respectively), underlining genetic similarity.

However, a genetic association of early-life vocabulary with educational attainment and intelligence emerged only during toddlerhood (e.g., receptive vocabulary and intelligence: rg = 0.36). Increased ADHD risk was genetically associated with larger infant expressive vocabulary (rg = 0.23). Multivariate genetic models in the ALSPAC (Avon Longitudinal Study of Parents and Children) cohort confirmed this finding for ADHD symptoms (e.g., at age 13; rg = 0.54) but showed that the association effect reversed for toddler receptive vocabulary (rg = −0.74), highlighting developmental heterogeneity.


The genetic architecture of early-life vocabulary changes during development, shaping polygenic association patterns with later-life ADHD, literacy, and cognition-related traits.

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