Amylo-1,6-glucosidase activity in cultured cells: a deficiency in type III glycogenosis with prenatal studies.

Deficiency of amylo-1,6-glucosidase activity was expressed in parallel in liver and skin fibroblasts from a patient with type III glycogenosis. In crude extracts of control liver and muscle, amylo-1,6-glucosidase (M.W. 164000) was identified by immunoprecipitation; no cross-reacting material was found in the patient's liver. Assay of amylo-1,6-glucosidase activity in cultured skin fibroblasts from the affected family revealed less than 10 per cent of control value in mutant homozygous cells whereas in cells from the parents, activity was reduced to 40-60 per cent of the control value. Activity in cultured amniotic fluid cells was similar to that of control fibroblasts. In cultured amniotic fluid cells obtained during the mother's subsequent pregnancy, the normal amylo-1,6-glucosidase activity measured, predicted correctly the outcome of this pregnancy prior to the 20th week of gestation.