In babies aged 15 to 18 months, a greater number of spoken words is genetically associated with an increased risk of attention deficit hyperactivity disorder.
- In babies aged 15 to 18 months, word production was linked to literacy, while in children aged 24 to 38 months, it was also associated with cognition.
- Increased risk of ADHD was genetically associated with a larger expressive vocabulary in 15- to 18-month-old infants. This link was reversed in older children.
- Toddlers with a higher genetic risk for ADHD may be inclined to express themselves more.
Typically, children begin to say their first words between 10 and 15 months of age. This is called “expressive vocabulary.” Around the age of two, they can produce between 100 and 600 words and understand many more. For comprehension purposes, this is called “receptive vocabulary”. Each child has their own language learning developmental path, resulting in individual differences. “Some variations in language acquisition may be linked to variations in the genetic code stored in our cells,” has indicated Beate St Pourcainresearcher at Radboud University in Nijmegen (Netherlands).
Vocabulary size at the start of life is hereditary
In a recent study, the scientist and her team wanted to examine the role of genetics in literacy (spelling, reading and phoneme awareness), cognition (general intelligence and years of education) and neurodevelopmental conditions , including attention-deficit/hyperactivity disorder (ADHD). To do this, they studied 37,913 parent-reported measures of vocabulary size (English, Dutch, Danish) for 17,298 children of European origin and genetic data from toddlers. Meta-analyses were conducted for early expressive (15 to 18 months), late expressive (24 to 38 months), and late receptive (24 to 38 months) vocabulary.
According to the results, published in the journal Biological Psychiatry, several genetic factors underlying vocabulary size in babies and toddlers have been identified. The team found that genetic associations with measures related to literacy, cognition, and ADHD later in life varied across development. Children’s word production was linked to reading and writing skills, such as spelling, but links with cognition were only found for toddlers’ vocabulary scores aged 24 to 38 months .
ADHD: Affected children may be likely to express themselves more
Children aged 24 to 38 months had some language proficiency and could “talk to learn.” This involves higher-level cognitive processing, while the development of verbal skills may begin earlier. Another finding: an increased risk of ADHD was genetically associated with a larger expressive vocabulary in babies aged 15 to 18 months. However, this genetic association was reversed in toddlers aged 24 to 38 months: a smaller number of words understood was associated with more ADHD symptoms.
According to the authors, children with a higher genetic risk for ADHD may be inclined to express themselves more. In contrast, during the “speaking to learn” phase, when vocabulary size is linked to cognition, higher genetic risk for ADHD may be associated with lower verbal and cognitive abilities.
“The genetic influences underlying vocabulary size change rapidly in less than two years during infancy. By adopting a developmental perspective, our findings provide insight into early etiological processes related to speech and language in health and troubles”concluded Beate St Pourcain.