Autism Spectrum Disorder Worsens Motor Impairments of Fragile X Children, Study Reports

Children with both fragile X syndrome and autism spectrum disorder (ASD) start showing greater motor impairments as early as 18 months of age when compared with those with fragile X but not ASD, a study finds.

These findings suggest that differing motor development may serve as a marker of ASD in children with fragile X, the researchers said.

The study, “Developmental divergence: motor trajectories in children with fragile X syndrome with and without co-occurring autism,” was published in the Journal of Neurodevelopmental Disorders.

ASD affects 50-70% of males with fragile X. Both of these conditions are characterized by motor impairments, which may contribute to the development of other hallmark features, such as disturbances in language and social communication.

In children with fragile X — which is the main genetic cause of autism — motor impairments often are one of the first notable signs of atypical development. However, gross motor skills are more delayed in children with both fragile X and ASD.

“Emergent evidence suggests that early motor impairments in some children may contribute to the development or enhanced severity of certain ASD features,” the researchers said.

Aiming to better understand motor function in fragile X patients with and without ASD, researchers at University of South Carolina and University of California San Francisco monitored 42 children with fragile X and 40 normally developing children until age 5. At the study’s start, the median age of children in the fragile X group was 15.6 months, while the median age in the control group was 9.5 months.

Among the children with fragile X, 24 — including 22 boys —had both fragile X and ASD; the remaining 18 children, including 8 boys, had fragile X only. 

The team assessed childhood development using the Mullen Scales of Early Learning, which assesses language, visual reception, and fine and gross motor skills. The parent-reported Vineland Adaptive Behavior Scales – 2nd Edition also was used to measure communication, socialization, daily living skills, and motor skills.

Because motor development itself is tied into overall cognitive development, the scientists also assessed potential differences in nonverbal cognitive abilities.

Gross motor skills are bigger movements that use the muscles in the arms, legs, torso, and feet — such as walking. Fine motor skills are small movements, such as holding a fork, that involve the small muscles of the fingers, toes, wrists, lips, and tongue.

Results showed that, compared with typically developing children, those with fragile X had significantly lower scores in gross and fine motor skills at nine months of age, regardless of having ASD. After controlling for cognitive function, children with both fragile X and ASD showed significantly slower motor development compared with those with fragile X only from 18 months of age. 

Fine motor skill scores followed a similar trend, with significant differences in comparison with typically developing peers starting earlier in the group with fragile X and ASD than in children with fragile X only (9 vs. 18 months). Also at 18 months, those with ASD averaged about 2 points lower in the fine motor skill assessment than did children only diagnosed with fragile X.

All of these differences tended to increase with time, and parent-reported scores followed very similar trends.

“Results indicate that fine and gross motor skill acquisition is impaired in children with [fragile X] + ASD relative to [fragile X]-only and [typically developing] children at early ages,” the researchers said.

It is of particular importance that the observed differences in motor development occurred independently of differences in cognitive development, the investigators said.

“The present study findings suggest that divergence in motor development may occur independently of cognitive impairment and therefore contribute to and/or serve as a marker of concurrent ASD in [fragile X],” they said.

The scientists also said future work should focus on the link between motor development and areas such as cognition, language, and attention. They also called for further research on “the underlying mechanisms and long-term consequences of motor impairments in [fragile X].”