In-utero detection of Pompe's disease

Human amniotic fluid alpha-glucosidase

Amniotic fluid in midpregnancy contains significant alpha-glucosidase activity. This enzyme is distinguishable from the lysosomal acid alpha-glucosidase, deficiency of which is associated with Pompe's disease. The two enzymes differ in optimum pH, thermal stability, electrophoretic migration, isoelectric point, molecular mass, and immunological response. Amniotic alpha-glucosidase is also different from the classical neutral form. Immuno-cross reactions suggest that the amniotic fluid enzyme has a double fetal origin: renal and intestinal. It seems that alpha-glucosidase in amniotic fluid is linked to lipids.

alpha-glucosidase activity in human leucocytes: choice of lymphocytes for the diagnosis of Pompe's disease and the carrier state

alpha-Glucosidase activity was assayed in polymorphonuclear cells and lymphocytes from human peripheral blood with 4-methylumbelliferyl-alpha-D-glucopyranoside as substrate in the presence of sodium taurocholate. The pH vs. activity curve of the alpha-glucosidase indicated that differential estimation between acid and neutral alpha-glucosidases was difficult to perform with polymorphonuclear cells, but easily accessible with lymphocytes. The use of peripheral blood lymphocytes for the enzymatic diagnosis of Pompe's disease seemed to be more reliable than the use of whole leucocytes; this also the case with a classical Pompe's patient. The lymphocytes from the parents had normal or low normal activity of acid alpha-glucosidase in the freshly isolated state, but when cultured with phytohaemagglutinin for 72 h, the stimulated lymphocytes of both parents showed about half the enzyme activity of the cultured controls. It was deemed possible in all probability to identify the carrier state by assay of the enzyme activity in phytohaemagglutinin-stimulated lymphocytes.

Prenatal diagnosis of inborn errors of metabolism

More than 50 inborn errors of metabolism can be diagnosed in the fetus. This is accomplished by evaluation of constituents of the cell free amniotic fluid or of cultured or uncultured amniotic fluid cells. Only those syndromes with specific abnormal contributions to amniotic fluid can be so diagnosed. Currently diagnosable diseases and their assay methods are reviewed. Such assay methods must be able to differentiate the unaffected heterozygote from the affected homozygote.

Two alpha-glucosidases in cultured amniotic fluid cells and their differentiation in the prenatal diagnosis of Pompe's disease

A sensitive fluorometric assay utilizing 4-methylumbelliferyl-alpha-D-glucopyranoside has been developed for the determination of alpha-glucosidase. The enhanced sensitivity was achieved by increasing the solubility of the substrate with a water miscible organic solvent. With this system, cultured amniotic fluid cells were found to have two major forms of alpha-glucosidase with somewhat overlapping acidic pH optima; one with pH optimum at 4.5 is deficient in Pompe's disease (type II glycogenosis), while one with pH optimum at 6.0 is not affected in this disease. Specificity for the pH 4 form of alpha-glucosidase was achieved by exploiting the greater thermal lability of the pH 6 enzyme. The pH 6 form of the enzyme was also detectable in freshly prepared extracts of cultured fibroblasts. The procedure is direct and simple and has been applied to the prenatal diagnosis in two pregnancies at risk for Pompe's disease.