OBJECTIVEGlycogen storage disease type II (GSD II, Pompe disease) is caused by the deficiency of acid alpha-glucosidase (GAA) that leads to lysosomal glycogen accumulation. Early diagnosis and treatment of GSD II are considered to be critical for maximum efficacy of the enzyme replacement therapy. The aim of this study was to introduce two reliable methods and to generate the reference range of GAA activity.

METHODThe assay of GAA activity was performed in dried blood spots (DBS) and mixed leukocytes with acarbose to eliminate isoenzyme interference and to generate the reference range. GAA activity was assayed in 700 specimens for DBS from normal subjects and 100 specimens for mixed leukocytes from normal subjects to set up reference range. GAA activity in the samples of 4 patients who were clinically suspected of GSD II and their parents were also assayed.

RESULTThe intra-run and inter-run precision of the DBS method was less than 10%. GAA activity tested by DBS was stable for 28 days between room temperature and -80 degrees C. The reference range of newborns and children-adults in DBS samples was 8.92 - 60.03 pmol/(punch x h) and 8.00 - 37.43 pmol/(punch x h), respectively. The reference range in mixed leukocytes samples was 12.56 - 50.26 nmol/(mg protein x h). Four patients were diagnosed as GSD II with the above-mentioned two methods.

CONCLUSIONThe determination of GAA activity in DBS is sensitive and time-saving, and is suitable for high throughput analysis and newborn screening for GSD II. The assay of GAA activity in mixed leukocytes is accurate, fast and specific, and is suitable for final diagnosis of GSD II.