Fine Motor Trajectories in Children with Fragile X Syndrome and Siblings of Children with Autism

Background: Early motor delays and atypical motor movements are associated with autism related outcomes including increased autism symptomatology for children with fragile X syndrome (FXS; Roberts et al., 2016a) and expressive language delays in at-risk siblings of children with autism (ASIBs; LeBarton & Iverson, 2013). In addition, children with FXS and ASIBS demonstrate divergent fine motor skills from one another at 24 months old, indicating a differential motor profile in these groups at high risk for ASD (Roberts et al., 2016b). However, little is known regarding developmental trends in fine motor skills in children with FXS compared ASIBs and whether this is a potential area for early identification of autism in FXS.

Objectives: The purpose of the two studies presented was to 1) compare longitudinal developmental trajectories of fine motor skills in children with FXS contrasted to unaffected ASIBS, and 2) to compare these trajectories between children with FXS, children with FXS and comorbid autism (FXS+ASD), and ASIBs.

Methods: Study 1 compared longitudinal fine motor trajectories between a larger FXS group (N=128; mean chronological age (CA) at initial assessment=17.60 months) and the non-ASD ASIB group (N=34; M initial CA=11.48). Study 2 examined fine motor trajectories between the FXS (N=27; M initial CA=15.07), FXS+ASD (N=13; M initial CA=22.84), and the non-ASD ASIB (N=34) groups. Groups were assessed annually between 5 and 60 months old. Measures included the Mullen Scales of Early Learning (MSEL, 1995) for both studies, and for study 2, data from the Autism Diagnostic Observation Schedule-2 (ADOS-2, Lord et al., 2000) was drawn for clinical best estimates of comorbid ASD. The subset of FXS participants in study 2 (n=40) and all ASIBS were evaluated for a clinical best estimate of ASD. Approximately 33% (n=13) of the FXS group were diagnosed with comorbid ASD (FXS+ASD), and ASIBS were confirmed as not meeting criteria for ASD. Multilevel models were estimated to examine fine motor trajectories between groups.

Results:

Study 1: Results indicated that the FXS group had lower fine motor skills (b=1.49, p=.0026) at 9 months of age as well as a decelerating trend in fine motor skills over time compared to the ASIBs (b=.025; p<.001). The FXS and ASIB demonstrated increasingly divergent trends, with the greatest fine motor discrepancy at 60 months (b=14.43; p<.001).

Study 2: The fine motor skills of the FXS group were lower than the ASIBs (b=2.59, p=.0001) at 9 months of age, but were similar to the FXS +ASD group. The FXS and FXS+ASD groups became gradually more divergent from ASIBs over time. The FXS and FXS+ASD groups were marginally different at 24 months (p=.059), and differed at each subsequent assessment, with the FXS+ASD group demonstrating lower rates fine motor skill acquisition over time.

Conclusions: Collectively, study findings indicate that fine motor skills are an area of marked delay for children with FXS, and in particular FXS+ASD, relative to ASIBs. These results also provide preliminary evidence that fine motor trajectories may serve as a potential early indicator of atypical development and autism risk in FXS.