In order to determine the status of Tay-Sachs disease carrier identification in Toronto, Canada, since a change was made in 1978 from testing in the context of large-scale community clinics (up to 1,200 individuals tested in 1 day) to a case-finding approach to screening, a sample of area Jews was surveyed by questionnaire. The results indicated that a trend has developed for individuals at risk to delay testing until pregnancy when carrier detection is technically more difficult and the time available for retesting and organizing prenatal diagnosis is limited. If the trend continues, the full potential of chorionic villus sampling (CVS) for the prenatal diagnosis of the disease will be difficult to realize.
We describe a method for isolating milligram quantities of the four neutral glycosphingolipids, glucocerebroside, lactosylceramide, traiosylceramide, and globoside, from human placental tissue. This procedure is carried out on a silicic acid column eluted with a continuous chloroform-methanol gradient (19:1 to 4:1); the four glycosphingolipids elute as separate fractions with no need for further separation. The method is simple, rapid, and yields sufficient material to use as analytical standards for several hundred runs. The lipids have been identified by NMR spectroscopy. Placental tissue is freely available in most centers and is an excellent untapped source for these compounds. Given that lactosylceramide is not commercially available and that triaosylceramide (ceramide trihexoside) cannot be obtained in a reliable state, this technique represents an effective solution to this dilemma.
Abstract In a child with enzymatically and histopathologically proven metachromatic leukodystrophy (MLD), the disease pursued a course typical of juvenile MLD characterized by neurological degeneration beginning at age 9 years and ending in death at age 18. A younger brother of the patient was found to have profound deficiency of arylsulfatase A in leukocytes and to excrete five‐ to 20‐fold greater than‐normal amounts of sulfatide in the urine. He was completely free of symptoms attributable to MLD until age 16 when he developed acute cholecystitis caused by sulfatide accumulation in the gallbladder. Results of detailed neurological examination at age 21 years were normal; formal psychometric assessment showed a full‐scale IQ of 105 (Wechsler). Studies on cultured skin fibroblasts from the brother showed defects in arylsulfatase A activity, measured with the use of synthetic and natural substrates, and in radiolabeled sulfatide turnover. Cellulose acetate gel electrophoresis of fibroblast extracts from the patient showed no detectable arylsulfatase A isozyme under conditions that clearly distinguished pseudo‐arylsulfatase A deficiency from classical MLD. Biochemically, the patient was indistinguishable from patients with classical MLD; on the other hand, his clinical course is dramatically more benign than that of his sister who was affected with severe MLD.
Heterozygotes for Tay-Sachs disease can be distinguished by measuring the serum hexosaminidase activity and calculating the percentage of the heat-labile (A) form. We tested 7565 Ashkenazi Jews in Metropolitan Toronto and found a carrier frequency of 0.071. This figure was similar to the predicted frequency on the basis of caseload over a five-year period. We also found that 15% of women taking oral contraceptives were false-positive carriers. As with pregnant women, these false-positive carriers could be distinguished from true carriers by assaying leukocyte hexosaminidases.
This chapter focuses on the enzymological diagnosis of lysosomal storage disorders. The simplest classification divides the lysosomal storage disease (LSDs) into three subgroups: (1) the sphingolipidoses, (2) the mucopolysaccharidoses, and (3) the oligosaccharidoses. Difficulties in accurate assessment of the role of a specific lysosomal hydrolase in the pathogenesis of a storage disease often result from problems associated with in vitro assays of enzymes. They include: (1) differences between natural versus synthetic substrates, (2) requirements for natural activator or co-hydrolase proteins, (3) presence of lysosomal and non-lysosomal hydrolases, (4) secondary effects on other enzymes resulting from the primary gene defect, and (5) the vagaries of demonstrating a gene-dose effect in heterozygotes. Lysosomal hydrolases may be analyzed using either the natural substrate for the particular enzyme or one of a number of synthetic substrates. The most common are the p-nitrophenyl or 4-methylumelliferyl (4MU) derivatives.
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