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

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