Prenatal detection of Pompe's disease

Rapid prenatal diagnosis of glycogen-storage disease type II by electron microscopy of uncultured amniotic-fluid cells

Glycogen-storage disease Type IIa is a fatal, genetically determined disease of infancy or early childhood that is characterized by deficient activity of acid alpha-glucosidase and by the presence of intracellular vacuoles full of glycogen, which are found in most tissues, including skin and liver. On electron microscopy these specific vacuoles are tightly packed accumulations of glycogen particles surrounded by a single membrane. We did electron-microscopical examinations on uncultured amniotic-fluid cells from 26 women whose fetuses were at risk for glycogen-storage disease Type IIa and from 8 normal control pregnant women. We found specific vacuoles in cells from 6 of the 26 high-risk patients. At delivery, glycogen-storage disease Type IIa was present in the infants of these 6 women and absent in those of the other 20 according to results of clinical, biochemical, and electron-microscopical studies of gestational products. After amniocentesis at 15 to 18 weeks of gestation, the prenatal diagnosis made by electron microscopy of uncultured amniotic-fluid cells was available in three to six days, whereas it took from three to six weeks to make the diagnosis by enzymatic analysis of the cultured amniotic-fluid cells. We conclude that the electron-microscopical prenatal diagnosis of glycogen-storage disease Type IIa is rapid, safe, and reliable. It should facilitate earlier diagnosis and thereby help to preserve parental options.

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.

A sensitive semi-automated kinetic assay of alpha-D-glucosidase for the prenatal diagnosis of type 2 glycogenosis (Pompe's disease)

Prenatal diagnosis of type 2 glycogenosis (Pompe's disease) has been done on cultured amniotic fluid cells, using a semi-automated fluorimetric kinetic assay for alpha-D-glucosidase with 4-methylumbelliferyl-alpha-D-glucoside as substrate. The activity of the enzyme was related to that of beta-D-galactosidase, and found to be absent in cells from an affected fetus. The diagnosis was confirmed in fetal liver, where the same assay was used to show absence of alpha-D-glucosidase activity with normal beta-D-galactosidase activity, and where increased glycogen deposition was demonstrated histologically. This type of assay is generally applicable to lysosomal enzymes, and to other fluorigenic enzyme reactions.

Prenatal diagnosis of mucolipidosis IV by electron microscopy

Mucolipidosis IV, a recently recognized metabolic storage disease, is characterized clinically by corneal opacity in infancy, full facial features, and psychomotor retardation. Electron microscopy of cells from a 2-year-old affected girl revealed multiple cytoplasmic storage bodies. Cultured amniotic fluid cells, in two subsequent pregnancies, demonstrated similar abnormal storage bodies. Electron microscopic examination of various uncultured tissues from one abortus demonstrated abnormal inclusions in the cells of the brain, cornea, conjunctiva, and other epithelial tissues, thus confirming the prenatal diagnosis. This suggests that mucolipidosis IV is an autosomal recessive trait and demonstrates the efficacy of electron microscopy in the prenatal diagnosis of metabolic storage diseases whose biochemical defect is yet unknown.

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.