Glycogen storage disease type II (GSD II, OMIM 232300), also known as Pompe’s disease, is an autosomal recessive disorder caused by a defect in acid-alpha-glucosidase (GAA) (EC 3.2.1.20/3) in the lysosome. GAA mainly hydrolyzes the glycogen alpha-1’4- and alpha-1’6-glycosidic bonds in lysosomes under acidic conditions, and its defect causes a large accumulation of glycogen in lysosomes, resulting in the proliferation and destruction of lysosomes and damage to the corresponding tissues and organs. The incidence of GSD II is approximately 1:40,000 in North America and Europe and 1:50,000 in Taiwan, China [1-3]; it is classified into infantile and late forms according to the age of onset and tissues involved. The infantile form is more severe and often presents with early postnatal onset and rapid progression of myocardial hypertrophy, muscle weakness, feeding difficulties, and respiratory distress, and the most common cause of childhood hypertrophic cardiomyopathy is GSD II. Patients with the infantile form develop myocardial hypertrophy and severe myocardial weakness in the first few months of life, progress rapidly, and often die of cardiopulmonary failure within 1-2 years of age. The late form often develops progressive muscle weakness and dyspnea in adolescence or adulthood, progresses slowly, and often dies of respiratory failure. The clinical manifestations of GSD type II patients are not specific, and GAA enzyme activity measurement is an important basis for its diagnosis. Although GAA is also expressed in peripheral blood leukocytes, the accuracy of the assay is affected by the interference of its isoenzymes Maltase glucoamlyse (MGA) and neutral glucosidase in neutrophils. However, the accuracy of the assay was affected by the interference of its isoenzyme Maltase glucoamlyse (MGA) and neutral glucosidase. After 2004, acarbose was used to selectively inhibit MGA activity, which significantly improved the accuracy and specificity of GAA determination. In 1999, recombinant GAA enzymes were used in clinical treatment, which significantly improved the survival time and quality of life of patients, but the efficacy of enzyme replacement therapy was limited in patients who had developed symptoms, and the families of patients had to bear the huge treatment costs. Even when receiving enzyme replacement therapy, the disease remains lethal [6]. To date, there are no reports of patients receiving enzyme replacement therapy in China. The high mortality rate of GSD II and the high cost of treatment have led to the need for some families to have another child, thus raising the need for prenatal diagnosis. Therefore, prenatal diagnosis of this disease is of great importance for parents to have normal children again. The prenatal diagnosis of GSD II mainly includes methods such as determination of GAA enzyme activity in amniotic fluid or chorionic hair tissue, morphological or genetic analysis of chorionic hair [7, 8]. In the present study, we performed a familial diagnosis and prenatal diagnosis for one GSD II family line with preexisting patients by two methods of fetal amniotic fluid cell enzyme activity assay combined with GAA gene mutation analysis.