Direct assay of iduronate-2-sulfatase for Hunter disease using UPLC-tandem mass spectrometry and fluorogenic substrate.

OBJECTIVE

We devised iduronate-2-sulfatase (IDS) enzyme activity assays by combining fluorometric substrate and LC-MS/MS based detection.

DESIGN AND

METHODS

4-Methylumbelliferyl α-L-idopyranosiduronic acid 2-sulfate (IDS-S) was used as a substrate for IDS. Its enzymatic product, 4-methylumbelliferyl α-L-idopyranosiduronic acid (IDS-P) and internal standard, 4-methylumbelliferyl α-L-idopyranoside (IDS-IS), were directly measured by UPLC-MS/MS. We determined the precision of our enzyme assay and the effects of sample amounts and incubation time based on the results. Dried blood spots (DBSs) of 110 normal newborns and three patients with Hunter disease were analyzed.

RESULTS

IDS-IS, IDS-P and IDS-S were fully separated using UPLC without any ion suppressions. The intra- and inter-assay precisions were 8.5-10.5% and 11.9-15.3%, respectively. The amount of product obtained was proportional to the number of DBSs and increased linearly with the incubation period from 0 to 15 h. The enzyme activities in DBSs from three patients with MPS II were markedly lower than those in the DBSs of 110 normal newborns.

CONCLUSION

To the best of our knowledge, this is the first report describing the use of LC-MS/MS for the diagnosis of Hunter disease with a commercially available substrate. Our method would be a rapid and effective screening tool for the diagnosis of Hunter disease with further study.