BackgroundEarly developmental milestones, such as the age at first walking or talking, are associated with later diagnoses of neurodevelopmental disorders, but the relationship to genetic risk for neurodevelopmental disorders are unknown. Here, we investigate associations between genetic liability to autism spectrum disorder (autism), attention deficit hyperactivity disorder (ADHD), and schizophrenia and attainment of early-life language and motor development milestones.MethodsWe use data from a genotyped sub-set (N = 15 205) of children in the Norwegian Mother, Father and Child Cohort Study (MoBa). In this sample, we calculate polygenic scores for autism; ADHD and schizophrenia and predict maternal reports of children’s age at first walking and talking, motor delays at 18 months, language delays at 3 years, and a generalized measure of concerns about development. We use linear and probit regression models in a multi-group framework to test for sex differences.ResultsADHD polygenic scores predicted earlier walking age in both males and females (β=-0.037, pFDR=0.001), and earlier first use of sentences (β=-0.087, pFDR=0.032) but delayed language development at 3 years in females only (β=0.194, pFDR=0.001). Additionally, we found evidence that autism polygenic scores were associated with later walking (β=0.027, pFDR=0.024) and motor delays at 18 months (β = 0.065, pFDR=0.028). Schizophrenia polygenic scores were associated with a measure of general concerns about development at 3 years in females only (β=0.132, pFDR=0.024).ConclusionsGenetic liabilities for neurodevelopmental disorders show some specific associations with measures of early motor and language development in the general population, including the age at which children first walk and talk. Associations are generally small and occasionally in unexpected directions. Sex differences are evident in some instances, but clear patterns across different polygenic scores and outcomes are hard to discern. These findings suggest that genetic susceptibility for neurodevelopmental disorders is manifested in the timing of developmental milestones in infancy.