Early motor trajectories in infants at increased genetic likelihood for autism

Infants 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, specific patterns of delay, and how these might relate to a future ASD diagnosis. In this study, we used a detailed gross motor infant assessment, the Alberta Infant Motor Scale (AIMS), to assess motor trajectories in the first year of life in EL-AutSib, EL-TSC, and a comparison group with low-likelihood of autism (LL).

Participants included 51 EL-AutSib, 26 LL, and 16 EL-TSC infants who were assessed on motor ability at 3, 6, 9, and 12 months of age using the AIMS. EL-AutSib participants were further categorized into autism (ASD) or no autism (nASD) groups based on clinical best estimate at 24 or 36 months of age. AIMS total scores were analyzed using a linear mixed-model to assess differences in motor development between groups over time.

EL-AutSib-ASD, EL-AutSib-nASD, and LL groups exhibited comparable growth in motor ability over 3-12 months of age. Though non-significant, LL participants on average had the highest AIMS total scores across timepoints, followed by EL-AutSib-nASD and EL-AutSib-ASD, respectively. EL-TSC participants scored significantly lower on the AIMS compared to the EL-AutSib-ASD group (ß=-7.92, p<0.001), with slower growth over time (ß=-0.80, p=0.04).

These findings identify distinct motor trajectories between two populations with an elevated genetic likelihood of developing ASD. EL-AutSibs displayed converging motor trajectories with the LL group irrespective of ASD outcomes, suggesting that motor milestones, even when examined more granularly, may not capture the full range of motor differences in EL-AutSibs. However, the AIMS captured early and persistent motor delays in EL-TSC infants, highlighting the clinical utility of this measure for populations with more significant developmental delays.