IntroductionInfants with an older sibling with autism spectrum disorder (ASD) (EL-AutSib) and infants with tuberous sclerosis complex (EL-TSC), a genetic neurodevelopmental syndrome highly associated with ASD, exhibit motor and other developmental differences in the first year of life. Despite the prevalence of gross motor impairments in these populations and the need for early clinical monitoring, there is little conclusive evidence of the onset of motor differences between these groups, specif