Assays / Genetic Enzymes / Arylsulphatase B

Principle Of Method: Hydrolysis of the synthetic substrate 4-nitrocatechol sulphate is measured under conditions designed to minimise interference from other arylsulphatases. The amount of product (4-nitrocatechol) formed is determined from the absorbance at 515 nm.

Uses And Limitations Of The Method: The enzyme is deficient in Maroteaux-Lamy disease (MPS type VI). Its natural function is to cleave sulphate groups from N-acetyl galactosamine residues in dermatan sulphate, and its alternative name is N-acetylgalactosamine-4-sulphate sulphatase. The deficiency can be shown in leucocytes and cultured fibroblasts from affected patients, and, taken with a demonstration of excessive urinary excretion of dermatan sulphate, the diagnosis is confirmed. ASB is also deficient in multiple sulphatase deficiency. Prenatal diagnosis of MPS VI is possible by measuring the enzyme in cultured amniotic cells and, theoretically, in cultured chorionic villi although the SAS has no experience of the latter. The laboratory does not offer prenatal diagnosis of MPS VI by direct analysis of chorionic villi.

Specimen Requirements: For preliminary testing, blood. 5 ml lithium heparin (orange capped tube) unseparated and unfrozen. Send at room temperature to arrive at the laboratory within 24h of venepuncture. For follow-up, fibroblasts cultured from a skin biopsy may be needed. Biopsy material should be collected aseptically into a sterile bottle containing tissue culture medium (available from the laboratory), and sent at room temperature to arrive within 24 hours, Biopsies for tissue culture should not be frozen. Fibroblast cultures established in other laboratories should be sent in plastic 25 cm² flasks filled with medium.

THE LABORATORY RECOMMENDS USE OF A COURIER SERVICE OR ROYAL MAIL SPECIAL DELIVERY FOR SENDING ALL SPECIMENS TO THE LABORATORY.

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