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Sandhoff disease is a GM2 gangliosidosis that is rare in Thailand. The authors report a Thai family with two children known to have infantile form of Sandhoff disease. The index case exhibited mitral valve prolapse with mitral regurgitation as an early sign, which is a rare presentation in Sandhoff disease. Thereafter the patient had developmental regression, startle reaction, and cherry red spots. The diagnosis was confirmed by biochemical analysis.

Two pairs of alleles, at the two loci of hexosaminidase (HEX), were found to segregate in an Arab inbred family: the normal and the mutant Tay-Sachs (TSD) alleles of HEX A, and the normal and a mutant allele of HEX B. Since the mutant HEX B is heat labile, no reliable identification of TSD genotypes can be obtained in its presence, as long as the proportions of HEX A and B are estimated by the routinely used heat-inactivation method. The genotypes may be correctly identified in such cases by separation of the two isoenzymes on ion-exchange chromatography, estimating their individual activities, and calculating the ratio between them. Of the nine genotype combinations possible with these two pairs of alleles, five have been identified in the reported family by this procedure.

Amniocentesis and subsequent tests are reported on a fetus conceived of a rare mating type: its mother has an intermediate level of beta hexosaminidase A (HEX A), characteristic of carriers of Tay-Sachs disease (TSD), while the father suffers from an adult-onset GM2 gangliosidosis (AOG) with severe HEX A deficiency. Activity of HEX A in the cultured fetal cells was very low when measured by the heat-inactivation method, thus showing the typical biochemical phenotype of TSD fetuses. However, upon separation of HEX isozymes by ion exchange chromatography, residual HEX A (17 per cent of total HEX) was demonstrated. Also in contrast to TSD fetuses, this fetus' fibroblasts were able to synthesize the precursor of alpha chains of HEX, and ultrastructural examination of its brain revealed few atypical lamellar bodies, unlike those found in TSD fetuses of the same gestational age. It is therefore concluded that the fetus was not affected with TSD, but rather with AOG.

Although reduced acid beta-glucosidase activity appears to be the primary enzyme defect in type I Gaucher disease, patients with this disorder also have marked elevation of serum acid phosphatase and beta-hexosaminidase activities but with a normal level of lactic dehydrogenase activity. Moreover, there is a characteristic alteration in the hexosaminidase isozyme distribution with a striking increase in hexosaminidase B. Since these changes appear to be consistent and unlike those associated with other disorders or the hormonally induced alterations associated with pregnancy, routine serum testing for the Tay-Sachs carrier state may offer a useful approach for the presumptive diagnosis and screening for Gaucher disease. Unlike the changes in affected homozygotes, there are no characteristic alterations of acid phosphatase or hexosaminidase in heterozygotes for Gaucher disease.

4-Methylumbelliferyl-6-sulfo-2-acetamido-2-deoxy-beta-D-glucopyranoside was synthesized and tested as a substrate for the diagnosis of GM2 gangliosidoses using leukocytes. Less than 2% of normal activity was measured in homogenates from patients with typical Tay-Sachs disease and from a patient with a variant form having 37% Hexosaminidase A by heat denaturation using the usual fluorogenic substrate. An adult patient had 8.5% of normal activity. Three patients with Sandhoff disease were found to have values ranging from 17% to 37% of normal. These values overlap the range found for carriers of Tay-Sachs disease, and suggest that the usefulness of this substrate, while excellent for diagnosing B variants of GM2 gangliosidosis, requires further study. Perhaps when used together with 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside excellent discriminations of patients, carriers and controls will be realized.

Measurement of hexosaminidase A activity in amniotic fluid was found to be a reliable diagnostic test in the prenatal diagnosis of Tay-Sachs disease. Including normal control specimens, analysis of 39 amniotic fluid samples have correctly predicted the condition of the fetus or, in pregnancies not yet come to term, have been in agreement with results from cultured cell extracts. In each case where both fluid and cultured cell extracts were analyzed, the results were in agreement. Analysis were performed by means of Cellogel, starch gel electrophoresis, polyacrylamide gel electrophoresis, or heat inactivation.

Activities and isozyme spectra of alpha-L-fucosidase and beta-D-hexosaminidase were similar both in biopsy material from fetal zone of placenta (chorion) and in chorion tissue obtained after abortion. Evaluation of the isozyme spectrum of these glycosidases in biopsy reeterial of chorion might be carried out for prenatal detection of fucosidosis (deficiency of alpha-L-fucosidase), Tay-Sachs disease (deficiency of hexosaminidase A) and of Sandhoff disease (deficiency of hexosaminidases A and B).

GM2 ganglioside labelled with tritium in the N-acetylneuraminic acid moiety was prepared and used to measure beta-hexosaminidase A activity in cultured humans skin fibroblasts extracts. The latter convert this substrate to the correspondingly labelled GM3 ganglioside which can easily be separated from the substrate by thin-layer chromatography. No cleavage of the N-acetylneuraminic acid group was observed under our conditions. Two methods are described for the determination of GM2-beta-hexosaminidase A activity in fibroblasts. The application of these methods to the diagnosis of Tay-Sachs disease is discussed.

Two consecutive pregnancies at risk for Tay-Sachs disease with heat-labile beta-hexosaminidase B were monitored. Differential isozyme detection of beta-hexosaminidase in cell free amniotic fluid by DEAE cellulose column chromatography and cellulose acetate paper electrophoresis showed an affected fetus in the first pregnancy and an unaffected in the second. These results were confirmed in the aborted fetus and in a newborn baby, respectively.

Prenatal diagnosis was carried out in 10 families suffering from lysosomal diseases: Tay-Sachs disease--5 families, Sandhoff disease--1 family, GM1-gangliosidosis--1 family and Hunter disease--3 families. Diagnosis of Tay-Sachs disease was excluded in fetuses of two families, Sandhoff disease--in one family, GM1-gangliosidosis--in one family, Hunter disease--in two families. Tay-Sachs disease was found in two fetuses and in one neonate. In two fetuses was found Hunter disease (twin pregnancy). The results of prenatal diagnosis were corroborated by postnatal studies of the neonates funicular blood and of autopsies of the aborted fetuses tissues. Application of several independent procedures for prenatal diagnosis of hereditary lysosomal diseases enabled to exclude erroneous diagnosis.

Hexosaminidase (Hex) A, B, and C/S were electrophoretically separated from cultured amniotic fluid cells, fetal brain, and white blood cells. Photographs of cellulose acetate zymograms were evaluated by reflectometric scanning. The usefulness and limitations of this rapid method were shown. Hex A was completely absent in the amniotic fluid cells of one out of three pregnancies at risk for Tay-Sachs disease, but Hex C/S was present in this case. The prenatal diagnosis of Tay-Sachs disease was made, and confirmed with the fetal material after abortion. Hex C/S was distinguishable from a residual or "heterozygous" Hex A activity. In the two other risk pregnancies, reflectometric Hex A activities were found to be 50 and 34% of control; the heterozygous stage was presumed for the fetuses.

Prenatal diagnosis for Tay-Sachs disease was performed on 25 patients using chorionic villus sampling (CVS). Nineteen were diagnosed as normal, and six were affected. Normal villus extracts had both hexosaminidase (hex) A and B activity, as determined by Cellogel and polyacrylamide gel electrophoresis, while extracts from affected fetuses had only hex B activity. Compared to cultured amniotic fluid cells or fibroblasts, villi contained less hex A. Hex A levels in fresh villi and cultured trophoblasts were roughly comparable.

We have prepared a new radiolabeled substrate (N-[3H]acetylglucosamine-glucuronic acid-N-[3H]acetylglucosamine), from hyaluronic acid, for an assay of beta-N-acetylhexosaminidase activity. Using this substrate, we found a striking deficiency of beta-N-acetylhexosaminidase activity in cultured skin fibroblasts and in liver homogenates from patients with Tay-Sachs disease. DEAE-cellulose chromatography at pH 6.0 revealed that both isoenzymes A and B of beta-N-acetylhexosaminidase from normal liver participated in the catabolism of hyaluronic acid. There were, however, major differences in substrate specificities between isoenzymes A and B. Our results indicate that this substrate should be useful for enzymatic diagnosis of Tay-Sachs disease.