A fluorimetric enzyme assay for the diagnosis of Sanfilippo disease C (MPS III C)

Both the α- and β-anomers of 4-methylumbelliferyl-D-glucosaminide were synthesized and shown to be substrates for the lysosomal acetyl-CoA: glucosaminide N-acetyltransferase. Using the β-anomer, fibroblasts and leukocytes from 11 different Sanfilippo C patients showed <1% of mean normal N-acetyltransferase activity. Heterozygotes showed intermediate activities. The enzymatic liberation of the fluorochrome from 4-methylumbelliferyl-β-d-glucosaminide requires the sequential action of the N-acetyltransferase and β-hexosaminidase. Normal β-hexosaminidase activity caused complete hydrolysis of the reaction intermediate 4-methylumbelliferyl-β-d-N-acetylglucosaminide formed by the N-acetyltransferase. In cell extracts with a β-hexosaminidase deficiency, however, a second incubation in the presence of excess β-hexosaminidase is needed to avoid underestimation of the N-acetyltransferase activity.

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