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Objective In order to make a well understanding on glycogen storage disease typeⅡ (GSDⅡ), this paper explored clinical features and genetic analysis of 7 patients with late-onset glycogen storage disease typeⅡ. Methods Clinical data of 7 patients with late-onset glycogen storage disease type Ⅱ were collected and acid α-glucosidase (GAA) gene sequencing was performed. Results Seven patients who belong to 4 families were at the age of 13-31 years old. The first symptom occurred at 6-17 years old, and the age at first and definitive diagnosis was 12-29 and 12-30 years old, respectively. The initial symptoms were mostly related to limb girdle muscular atrophy and weakness. The GAA activity ranged from 0 to 5.27 nmol/(mg·h). Sequencing analysis revealed 14 sequence variants, including 2 novel mutations (Q81X and c.1355_1356delC), 2 pseudodeficiency alleles (G576S and E689K), 8 polymorphic loci, and 2 sequence variants previously related with glycogen storage disease type Ⅱ pathogenesis (W746C and D645E). Conclusions Due to the apparently diagnostic delay, prognosis of patients with glycogen storage disease type Ⅱ could be improved by increasing the clinician's awareness of the disease. It is essential to combine clinical history with GAA activity and GAA gene analysis when we make a definitive diagnosis of glycogen storage disease type Ⅱ. Though siblings share the same set of GAA mutations, the phenotype regarding the course and severity of disease could vary substantially. doi: 10.3969/j.issn.1672-6731.2014.05.008