a. Proportion of mice able to perform at two different speeds on a motorized treadmill. There was a significant overall difference in performance between groups (10cm/s, P=0.0013; 25cm/s, P<0.0001; Fisher’s exact test). Post hoc pairwise comparison of AAV9/MECP2-treated and AAV9/GFP-treated mice showed a difference at 25cm/s (P=0.024), but not at 10cm/s. b-e. Open field tests performed at 9 weeks following AAV9 injection showing measures for movement duration (b), mean velocity (c) and total distance moved (d) together with rearing frequency (e). f. Representative whole-body plethysmograph traces showing regular and erratic breathing patterns/apnoeas (arrows) in WT and Mecp2-/y mice respectively. g. Apnoea frequency, h. baseline breathing frequency, i. breathing frequency variability. Both open field and respiratory measures were assessed by 2-way ANOVA with Tukey’s post hoc comparisons. *P<0.05, **P<0.01, ns=not significant. Numbers of animals per genotype/treatment group are shown within each bar.