Debranching enzyme in fibroblasts, amniotic fluid cells and chorionic villi: pre- and postnatal diagnosis of glycogenosis type III.

Glycogenosis type III is characterized by a deficiency of debranching enzyme in most tissues, and it can be detected by the inability to liberate glucose from limit dextrin. However, using this assay, the deficiency is not expressed in cultured fibroblasts from patients with glycogenosis type III. We have demonstrated that the failure to detect debranching enzyme deficiency in fibroblasts is entirely due to interference of acid alpha-glucosidase, which can also hydrolyse limit dextrin. A method is described to remove specifically acid alpha-glucosidase allowing clear discrimination between fibroblasts from patients and controls, whereas heterozygotes showed intermediate values. The results with amniotic fluid cells and chorionic villi suggest the feasibility of first- and second-trimester prenatal diagnosis of glycogenosis III.