Motor phenotypes associated with genetic neurodevelopmental disorders.

Objective: There is a growing number of monogenic disorders implicated in neurodevelopmental disorders (NDDs), including autism spectrum disorder and intellectual disability. Motor impairment is frequently seen in these disorders, although not clearly defined. We aimed to characterize the motor phenotype of genetic NDDs.

Methods: We analyzed data from Simons Searchlight, collecting information on patients with genetic NDDs. Data analyzed included Vineland Adaptive Behavior Scales Second Edition (Vineland-II) motor standard scores, motor milestones and tone abnormalities.

Results: In total, 959 patients with 57 genetic disorders were included. Disorders associated with Vineland-II motor standard score <56 included GRIN2B-related disorder (mean standard score = 53.5), HNRNPH2-related disorder (mean standard score = 55.8) and SCN2A-related disorder (mean standard score = 49.9). The only genetic condition with a mean age of sitting unsupported ≥18 months was GRIN1-related disorder (mean age = 26.3 months). Genetic conditions with a mean age of walking independently ≥36 months included CTNNB1-related disorder (mean age = 37.4 months) and HNRNPH2-related disorder (mean age = 41.9 months). Tone abnormalities included hypotonia in 83% (577/696), hypertonia in 16% (112/696), a diagnosis of cerebral palsy (CP) in 10% (73/696) and a diagnosis specifically of spastic CP in 3% (23/696).

Interpretation: Patients with genetic NDDs have a spectrum of motor impairment, which warrant further characterization.