Rett syndrome is a pervasive neurodevelopmental disorder associated with a pathogenic mutation on the MECP2 gene. Impaired movement is a fundamental component and the Rett Syndrome Gross Motor Scale was developed to measure gross motor abilities in this population. The current study investigated the validity and reliability of the Rett Syndrome Gross Motor Scale. Video data showing gross motor abilities supplemented with parent report data was collected for 255 girls and women registered with the Australian Rett Syndrome Database, and the factor structure and relationships between motor scores, age and genotype were investigated. Clinical assessment scores for 38 girls and women with Rett syndrome who attended the Danish Center for Rett Syndrome were used to assess consistency of measurement. Principal components analysis enabled the calculation of three factor scores: Sitting, Standing and Walking, and Challenge. Motor scores were poorer with increasing age and those with the p.Arg133Cys, p.Arg294* or p.Arg306Cys mutation achieved higher scores than those with a large deletion. The repeatability of clinical assessment was excellent (intraclass correlation coefficient for total score 0.99, 95% CI 0.93–0.98). The standard error of measurement for the total score was 2 points and we would be 95% confident that a change 4 points in the 45-point scale would be greater than within-subject measurement error. The Rett Syndrome Gross Motor Scale could be an appropriate measure of gross motor skills in clinical practice and clinical trials.

Women with RTT are very dependent on caregivers who maintain and rehabilitate their functional abilities. They can often walk short distances unassisted, but do have trouble transferring and thus getting up from a chair on their own. They have severe problems communicating and they often perform subtle signs that can be difficult to recognize. Implications for rehabilitation 3/4 of aging RTT women are household ambulators - daily training of motor functions and focus on assisting the initiation of movements are needed lifelong to maintain walking ability and participation in daily activities More than half of aging women with RTT can grab on to things - persons with hand function should be motivated to use this ability in the context of eating Communication is a difficult task especially for the aging RTT women - Communicative signs, their meaning and how to react to them should be written down for every woman in an easy accessible way to all caregivers The majority of aging RTT women can point out things of interest - they should be given the opportunity to participate in choice making.

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