Reliability and stability of cerebral palsy classification scales for individuals with <scp> <i>STXBP1</i> </scp> ‐ and <scp> <i>SYNGAP1</i> </scp> ‐related disorders

AIM: To determine the interrater reliability and stability of the Gross Motor Function Classification System (GMFCS), Manual Ability Classification System (MACS)/Mini-MACS, and Communication Function Classification System (CFCS) in individuals with STXBP1- and SYNGAP1-related disorders. METHOD: Data were collected from 83 individuals with STXBP1-related disorders (34 females, 49 males; mean age = 9 years 10 months) and 101 individuals with SYNGAP1-related disorders (51 females, 50 males; mean age = 10 years 11 months) who participated in a prospective natural history study with both cross-sectional and longitudinal phases. Two raters completed the GMFCS, MACS/Mini-MACS, and CFCS assessments on the same day; test-retest stability was evaluated for participants with two longitudinal assessments. RESULTS: Interrater agreement varied from 73.8% to 77.3% for the STXBP1-related disorder cohort and from 60.5% to 83.3% for the SYNGAP1-related disorder cohort. Interrater reliability weighted kappa scores for the STXBP1-related disorder cohort varied from 0.83 to 0.93, while scores for the SYNGAP1-related disorder cohort ranged from 0.66 to 0.81. Test-retest stability scores for the STXBP1-related disorder group varied from 0.62 to 0.94, while scores for the SYNGAP1-related disorder group ranged from 0.38 to 0.78. Significant correlations were found between all assessment scales for both STXBP1-related disorders (Kendall's tau range from 0.25 to 0.42) and SYNGAP1-related disorders (Kendall's tau range from 0.19 to 0.45). INTERPRETATION: The GMFCS, MACS/Mini-MACS, and CFCS demonstrate appropriate levels of interrater reliability and stability for individuals with STXBP1- and SYNGAP1-related disorders.