The reduction in acid α-glucosidase activity, measured in cultured fibroblasts (1.6 nmol/mg/h, normal values 64.4 ± 22.9), and the molecular analysis of the GAA gene that showed a homozygous mutation (C1124G> T/C1124G> T) confirmed the diagnosis of Pompe disease. Here, GAA is linked to glycogen storage disease II.