Longitudinal trajectory of gross motor skills in school-aged children with Rett syndrome

Background: In children with Rett syndrome, this study aimed to (1) describe gross motor skill trajectories; and (2) analyse the influences of genetic variant and comorbidities. Methods: This was a prospective longitudinal study conducted at the Danish National Center for Rett Syndrome 2008 to 2022. The Rett Syndrome Gross Motor Scale (RSGMS) was administered, and clinical data collected at each visit. Mixed-effects linear regression models were used to analyze the effects of age, genetic variant and comorbidities on gross motor skills. Clinical records data were reviewed. Results: Data for 33 children with a mean age of 7.3 years (SD 1.2) at first visit were followed for a mean duration of 6.8 years (SD 2.1). The mean RSGMS score was 24.0 (SD 13.2, total of 45) at baseline. Adjusting for age and genetic variant, all severity levels of epilepsy, autonomic breathing dysfunction and scoliosis, except for surgically corrected scoliosis, were associated with a 4-point decrease in RSGMS score every 5 years. Acute escalation of seizures, change in muscle tone, orthopedic surgeries and bone fracture could be associated capacity to maintain gross motor skills. Conclusion: We identified decline in gross motor skills during childhood. This novel natural history data can assist with interpretation of changes in gross motor skills following the administration of new therapeutics.