This is in agreement with previous work in which PDE-levels of the forearm muscles did not correlate with age in ambulant DMD patients and did not show an increase over one year time.[13, 14] This hypothesis is also strengthened by our own results in the other muscles which did not show a change in PDE-levels over a two-year time period and by the significant correlation with age in the TP muscle at baseline. Here, ALDH7A1 is linked to Duchenne muscular dystrophy.