Assays / Genetic Enzymes / a-N-Acetylglucosaminadase

Principle of Method:
Hydrolysis of the synthetic substrate 4-methylumbelliferyl-2-acetamido-2-deoxy-a-D-glucopyranoside at acid pH is followed by measuring the fluorescence of the liberated 4-methylumbelliferone after stopping the reaction with alkaline buffer.

Uses and Limitations of the Method:
Deficiency of lysosomal a-N-acetylglucosaminidase is the primary defect in Sanfilippo disease type B (MPS IIIB). Its natural function is to cleave á-linked N-acetylglucosamine residues in heparan sulphate. In its absence there is storage of heparan sulphate in the tissues and excess excretion in the urine. The deficiency can be shown in plasma, serum or cultured fibroblasts from MPS IIIB patients. White cells are not recommended for the diagnosis because of their low normal activity. The enzyme will usually be measured after excess heparan sulphaturia has been found to confirm the type of MPS III (A, B, C or D). It is the most readily assayed enzyme of the four involved in MPS III, and is usually the first to be assayed for this reason, although MPS IIIB is in fact rare in the UK. It is noteworthy that the enzyme is often found to be elevated in serum or plasma from MPS IIIA patients. Prenatal diagnosis of MPS IIIB is possible by analysis of chorionic villi or cultured amniotic cells; when amniocentesis is performed investigation of the GAG pattern in the supernatant fluid may also assist in the diagnosis. Most heterozygotes display diminished activity in serum or plasma and carrier detection may be possible in extended families.

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.

Back to Lysosomal Storage Disorders Index

Back to Alphabetical List of Assays Available