Abstract
AIM: To determine the interrater reliability and stability of the Gross Motor Function Classification System (GMFCS), mini-Manual Ability Classification System (mini-MACS), Manual Ability Classification System (MACS), and Communication Function Classification System (CFCS) in individuals with STXBP1 -Related Disorder ( STXBP1 -RD) and SYNGAP1 -Related Disorder ( SYNGAP1 -RD). METHODS: Data were collected from 83 individuals with STXBP1 -RD (mean age = 9.8 years) and 101 individuals with SYNGAP1 -RD (mean age = 10.9 years). Two raters completed the GMFCS, MACS/MiniMACS, and CFCS assessments on the same day, and test-retest stability was evaluated for participants with two longitudinal assessments. RESULTS: Interrater agreement varied from 73.8% to 77.3% for the STXBP1 -RD cohort and from 60.5% to 83.3% for the SYNGAP1 -RD cohort. Interrater reliability weighted kappa scores for the STXBP1 -RD cohort varied from 0.83 to 0.93 while the SYNGAP1 -RD cohort ranged from 0.66-0.81. Test-retest stability scores for the STXBP1 -RD group varied from 0.62 to 0.94 while the SYNGAP1 -RD group ranged from 0.38 to 0.78. Significant correlations were found between all assessment scales for both STXBP1 -RD (Kendall's Tau range from 0.25-0.42) and SYNGAP1 -RD (Kendall's Tau range from 0.19-0.45). INTERPRETATION: The GMFCS, MACS/MiniMACS, and CFCS demonstrate appropriate levels of interrater reliability and stability for individuals with STXBP1 -RD and SYNGAP1 -RD. WHAT THIS PAPER ADDS: Classification tools are reliable and stable in individuals with STXBP1 -RD and SYNGAP1 -RD. Gross motor function is least affected for both conditions.Language function is most affected for both conditions.Correlations are decreased compared to children with cerebral palsy due to phenotype differences.