The associations between autistic and communication traits in parents and developmental outcomes in children at familial risk of autism at 6 and 24 months of age

•Parent communication and autistic-like traits are related to offspring communication and autism severity.•These associations were found to emerge in childhood, however, we know very little about such associations in infancy.•We explored how parent communication and autistic-like traits are related to child development at 6 and 24 months of age.•Associations between parent variables and child social-emotional competence emerge as early as at 6 months of age.•These findings can have important implications for how we monitor child development and what interventions we administer. Several studies have explored relationships between parent broader autism phenotype and offspring communication, and have reported that autistic-like traits in parents are related to offspring communication difficulties and autism severity. However, past research has focused on studying such associations in childhood and we know very little about them in infancy. With accumulating evidence that interventions administered during infancy may be most effective in reducing ASD symptoms, it is imperative to examine whether relationships between parent autistic-like traits and child communication appear even earlier during this critical period of life. This longitudinal study collected data from infant siblings of autistic children (N = 32) and infants with no family history of autism (N = 45) to explore how autistic-like traits in parents related to child developmental outcomes during infancy. Parental communication difficulties and autistic-like traits were found to be associated with a range of child behaviours in the first two years of life, including social-emotional difficulties at 6 and 24 months, lower communication and emerging cognition at 24 months, and increased autistic behaviours at 24 months. Based on the results, it appears that some of the difficulties seen in parents are relayed to children genetically. These findings contribute to ASD research concerning early communication development in children and heritability of ASD traits and may have important implications in monitoring child development. Furthermore, since the current study found a significant association between autistic traits in parents and child social-emotional behaviour as early as 6 months of age, it provides evidence of the value of assessing interventions that target infancy.