Validation of a modified version of the gross motor function measure in PPPR5D related neurodevelopmental disorder.

The GMFM is a valid measure for characterizing motor function in individuals with PPP2R5D related neurodevelopmental disorder. The GMFM-66 had strong associations with the RULM and timed function tests which characterized gross motor, upper limb and ambulatory function demonstrating concurrent validity. The GMFM-66 was also able to differentiate between functional levels in PPP2R5D related neurodevelopmental disorder demonstrating discriminant validity. Future studies should examine its sensitivity to change over time, ability to identify sub-phenotypes, and suitability as an outcome measure in future clinical trials in individuals with PPP2R5D variants.