Recently, several promising treatments have emerged for neuromuscular disorders, 
highlighting the need for robust biomarkers for monitoring therapeutic efficacy 
and maintenance of the therapeutic effect. Several studies have proposed 
circulating and tissue biomarkers, but none of them has been validated to 
monitor acute and long-term drug response. We previously described how the 
myostatin (MSTN) level is naturally downregulated in several neuromuscular 
diseases, including Duchenne muscular dystrophy (DMD). Here, we show that the 
dystrophin-deficient Golden Retriever muscular dystrophy (GRMD) dog model also 
presents an intrinsic loss of Mstn production in muscle. The abnormally low 
levels of Mstn observed in the GRMD dog puppies at 2 months were partially 
rescued at both mRNA and protein level after adeno-associated virus 
(AAV)-microdystrophin treatment in a dose-dependent manner. These results show 
that circulating Mstn is a robust and reliable quantitative biomarker, capable 
of measuring a therapeutic response to pharmaco-gene therapy in real time in the 
neuromuscular system, as well as a quantitative means for non-invasive follow-up 
of a therapeutic effect. Moreover, a 2-year follow-up also suggests that Mstn 
could be a longitudinal monitoring tool to follow maintenance or decrease of the 
therapeutic effect.