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Abstract:
Mastering developmental milestones such as infant motor and personal-social skills (including social routines and pretend-play) can initiate a cascade of developmental changes that may affect language learning. Specifically, motor development may represent an important, but little understood “gateway” enabling children to interact with their environment. Here, we investigate how infant motor and personal-social abilities link to infant and toddler language performance, using a genetic perspective. For this, we studied measures of motor and personal-social skills (6 and 15 months) as predictors of language development, captured by ten language phenotypes (15-38 months) in genotyped children from the Avon Longitudinal Study of Parents and Children (N≤7,017). Language measures were combined into language factor scores (LFS) using structural equation modelling. Developmental genomic and non-genomic (residual) relationships across phenotypes were modelled with a Cholesky decomposition using genetic-relationship-matrix structural equation modelling (GRM-SEM). The ten early language measures were captured by three interrelated language factors (F-15M, F-24M, F-38M, 51.3% explained variance), each corresponding to a different age window. Across infant predictors and derived language factor scores, common genetic variation accounted for a modest proportion of the phenotypic variance (known as heritability, h2: gross-motor-abilities-6M-h2=0.18(SE=0.06), personal-social-skills-15M-h2=0.18(SE=0.06), LFS-15M-h2=0.12(SE=0.05), LFS-24M-h2=0.21(SE=0.06), LFS-38M-h2=0.17(SE=0.05)). Fitting a Cholesky GRM-SEM across predictors and LFS showed that infant gross motor abilities shared genetic influences with personal-social skills (factor loading λ; personal-social-skills-15M-λ=0.22(SE=0.09)), but were unrelated to language performance (P≥0.05). In contrast, genetic influences underlying personal-social skills, independent of gross motor skills, were related to all three LFS (LFS-15M-λ=0.26(SE=0.09), LFS-24M-λ=0.28(SE=0.10), LFS-38M-λ=0.30(SE=0.10)). GRM-SEM analyses studying individual language outcomes provided consistent results, both for genomic and non-genomic structures. Thus, aetiological processes linking motor to personal-social skills differ from those linking personal-social to language abilities, consistent with a developmental cascade where motor control enables children to engage in novel social interactions, but children’s social learning abilities foster language development.
