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

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‐ α GlcNS to MU‐ α GlcNH 2 and further hydrolysis during a second incubation is required to liberate 4‐methylumbelliferone, which can be measured. Yeast α ‐glucosidase, which has low but sufficient α ‐glucosaminidase activity, was used to hydrolyse the reaction intermediate MU‐ α GlcNH 2 to release 4‐methylumbelliferone and free glucosamine.