A fluorimetric enzyme assay for the diagnosis of sanfilippo disease type A (MPS IIIA)

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Abstract
Summary: 4‐Methylumbelliferyl‐α‐d‐N‐sulphoglucosaminide (MU‐α‐GlcNS) was synthesized and shown to be a substrate for the lysosomal heparin sulphamidase. Sanfilippo A patients' fibroblasts (n=42) and lymphocytes (n=1) showed 0–3% of mean normal heparin sulphamidase activity; in total leukocytes from patients (n=8) sulphamidase activity was clearly deficient. In fibroblasts from obligate heterozygotes for Sanfilippo A, the sulphamidase activity was reduced in 9 out of 10 cases. Heparin sulphamidase desulphates MU‐αGlcNS to MU‐αGlcNH2 and further hydrolysis during a second incubation is required to liberate 4‐methylumbelliferone, which can be measured. Yeastα‐glucosidase, which has low but sufficientα‐glucosaminidase activity, was used to hydrolyse the reaction intermediate MU‐αGlcNH2 to release 4‐methylumbelliferone and free glucosamine.