Fig. 1

Six-minute walk test (6MWT) distance over time in children (a) and adults (b) and 3-min stair climb test (3MSCT) results over time in children (c) and adults (d). Arrows indicate ages at initiation of enzyme replacement therapy (ERT). In cases 4, 5, 7, 8, 9, and 10, the first 6MWT measurement was recorded at or before initiation of ERT; baseline 3MSCT data were available for cases 4, 5, 8, and 10. All other data were collected after initiation of ERT. The dashed line in figure A represents normal 6MWT distances by age for children 4–11 years old [13]. Error bars represent standard deviations