The developmental genetic architecture of vocabulary skills during the first three years of life: Capturing emerging associations with later-life reading and cognition

Abstract

Individual differences in early-life vocabulary measures are heritable and associated with subsequent reading and cognitive abilities, although the underlying mechanisms are little understood. Here, we (i) investigate the developmental genetic architecture of expressive and receptive vocabulary in early-life and (ii) assess timing of emerging genetic associations with mid-childhood verbal and non-verbal skills. We studied longitudinally assessed early-life vocabulary measures (15–38 months) and later-life verbal and non-verbal skills (7–8 years) in up to 6,524 unrelated children from the population-based Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. We dissected the phenotypic variance of rank-transformed scores into genetic and residual components by fitting multivariate structural equation models to genome-wide genetic-relationship matrices. Our findings show that the genetic architecture of early-life vocabulary involves multiple distinct genetic factors. Two of these genetic factors are developmentally stable and also contribute to genetic variation in mid-childhood skills: One genetic factor emerging with expressive vocabulary at 24 months (path coefficient: 0.32(SE = 0.06)) was also related to later-life reading (path coefficient: 0.25(SE = 0.12)) and verbal intelligence (path coefficient: 0.42(SE = 0.13)), explaining up to 17.9% of the phenotypic variation. A second, independent genetic factor emerging with receptive vocabulary at 38 months (path coefficient: 0.15(SE = 0.07)), was more generally linked to verbal and non-verbal cognitive abilities in mid-childhood (reading path coefficient: 0.57(SE = 0.07); verbal intelligence path coefficient: 0.60(0.10); performance intelligence path coefficient: 0.50(SE = 0.08)), accounting for up to 36.1% of the phenotypic variation and the majority of genetic variance in these later-life traits (≥66.4%). Thus, the genetic foundations of mid-childhood reading and cognitive abilities are diverse. They involve at least two independent genetic factors that emerge at different developmental stages during early language development and may implicate differences in cognitive processes that are already detectable during toddlerhood. Differences in the number of words young children produce (expressive vocabulary) and understand (receptive vocabulary) can be partially explained by common genetic variation, and are related to reading and cognitive abilities later in life. Here, we studied genetic influences underlying expressive and receptive vocabulary during early development (15–38 months) and their genetic relationship with mid-childhood reading and cognitive skills (7–8 years), based on longitudinal phenotype measures and genome-wide genetic data from up to 6,524 unrelated children. We showed that early-life vocabulary skills are influenced by multiple independent genetic factors, of which two also relate to mid-childhood skills, suggesting developmental stability. One genetic factor emerging with expressive vocabulary at 24 months was linked to subsequent verbal abilities, including vocabulary measures at 38 months, as well as mid-childhood reading and verbal intelligence performance. A second, independent genetic factor related to receptive vocabulary at 38 months contributed more generally to variation in mid-childhood reading, verbal and non-verbal intelligence. Thus, the genetic foundations of mid-childhood reading and cognitive abilities involve at least two independent genetic factors that emerge during early-life language development and may implicate differences in overarching cognitive mechanisms.