Assays / Genetic Enzymes / Iduronate Sulphatase

Principle of Method: A [³H]-labelled disulphated disaccharide prepared from heparin is used as substrate. Upon action of the sulphatase this is converted to a monosulphated disaccharide which is separated by ion-exchange chromatography on ECTEOLA cellulose and determined by scintillation counting.

Uses and Limitations of the Method: Deficiency of this enzyme is the primary defect in mucopolysaccharidosis (MPS) type II (Hunter disease). This disease is characterised by increased glycosaminoglycan (GAG) excretion in urine, predominantly of dermatan and heparan sulphates and some heparin, and the sulphatase is assayed to confirm the diagnosis suggested by the GAG results. Severe and mild forms of the disease exist, but they cannot be distinguished by enzymatic analysis. Hunter disease is X-linked and some carriers have intermediate activity, but normal activity may not exclude the carrier state. Prenatal diagnosis is possible by direct enzymatic analysis of chorionic villi, amniotic fluid supernatant or an extract of cultured amniotic cells. The enzyme is also deficient in multiple sulphatase deficiency.

Specimen Requirements: Blood. 5 ml lithium heparin (orange capped tube) unseparated and unfrozen. Send at room temperature to arrive at the laboratory within 24h of venepuncture.

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

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