GAA and Glycogen storage disease due to acid maltase deficiency: It is caused by an autosomal recessive inherited deficiency of the lysosomal enzyme acid alpha glucosidase (GAA) and is estimated to affect 1:40 000 individuals.1 GAA deficiency leads to intralysosomale and intracellular accumulation of glycogen, alteration of autophagy and cell signaling, and consecutively to progressive skeletal and cardiac muscle cell dysfunction and death.2, 3, 4, 5 The phenotypic spectrum is broad and ranges from classic infantile Pompe disease (IOPD) to attenuated, late onset forms (LOPD).