Leveraging epigenetics to examine differences in developmental trajectories of social attention: A proof-of-principle study of DNA methylation in infants with older siblings with autism.

•Studying mechanisms underpinning ASD might benefit from incorporating epigenetic analysis into infant-sibling designs.•DNA methylation levels associated with early social attention are linked to genes involved in brain development and ASD.•Significant changes in the association between DNA methylation and behaviour were observed between 8 and 15 months.•Examining DNA methylation in age-homogeneous samples might allow to detect meaningful signals in relatively small samples.