Early language development is a crucial indicator of a child’s future language skills, reading abilities, and overall learning aptitude. Difficulties in language learning can often be linked to neurodevelopmental disorders like ADHD and ASD. Children typically begin speaking their first words between 10 and 15 months old, and by the age of two, they may have a vocabulary of 100 to 600 words. Each child follows their unique developmental path in language acquisition, leading to significant individual differences.
Senior researcher Beate St Pourcain emphasizes that genetic factors may play a role in language development. To explore this further, the team conducted a genome-wide meta-analysis study on vocabulary size in infants (15-18 months) and toddlers (24-38 months). Parents reported the words their children could say and understand from a predetermined list. The study included data from 17,298 English, Danish, or Dutch-speaking children, with information on spoken words available for both infants and toddlers, and understood words only available for toddlers.
The study also examined later-life outcomes, such as literacy, cognition, and neurodevelopmental conditions, using genetic summary data from large consortia. The researchers identified multiple genetic factors influencing vocabulary size in infants and toddlers, with associations with literacy, cognition, and ADHD-related measures changing as children develop. Toddlers, who have developed some language fluency, may “speak to learn” involving higher cognitive processing, while infants may be in the phase of “learning to speak.”
The researchers found that a larger number of spoken words in infancy was genetically associated with an increased risk of ADHD, whereas a smaller number of understood words in toddlerhood was linked to more ADHD symptoms. This suggests a shift in genetic relationships as children progress in their language development. The findings highlight the importance of early vocabulary assessment for future behavior and cognition, underscoring the need for more data collection efforts during infancy and toddlerhood.
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