Monitoring of dipeptidyl peptidase-IV (DPP-IV) activity in patients with mucopolysaccharidoses types I and II on enzyme replacement therapy - Results of a pilot study.

OBJECTIVES: Mucopolysaccharidoses (MPSs) are a group of rare, inherited metabolic disorders which result from the lack of one of the lysosomal enzymes responsible for the degradation of glycosaminoglycans. Early recognition of MPS is important as it enables prompt implementation of enzyme replacement therapy (ERT). Dipeptidyl peptidase-IV (DPP-IV) is a ubiquitous ectopeptidase which activity has been associated with the cell surface protein CD26. Our aims were to investigate plasma DPP-IV activity in untreated patients with MPS type II in comparison to control individuals and to evaluate changes of DPP-IV during ERT in MPS I or II patients.

DESIGN AND METHODS: One MPS I and five MPS II patients were treated with ERT for up to 19 months. DPP-IV activity was measured in plasma with a colorimetric method using Gly-Pro-p-nitroanilide as a substrate. The reference intervals were observed in 17 healthy donors and in 9 MPS II individuals before ERT implementation.

RESULTS: DPP-IV activity ranged from 557 to 1959 nmol/ml/h (median and interquartile range: 1453 [955– 1554], n = 17) in plasma of control samples. In 9 untreated MPS II individuals, DPP-IV activity was higher and ranged from 2565 to 5968 nmol/ml/h (median and interquartile range: 4458 [4031–5161]). In 6 MPS patients receiving ERT, DPP-IV activity ranged from 2984 to 8628 nmol/ml/h. No declining tendency was observed during the treatment.

CONCLUSIONS: DPP-IV activity is a good, newa nd valuable biomarker distinguishing between MPS and healthy individuals. However, it is not a useful marker of treatment efficacy and is unsuitable for monitoring.