Incomplete biomarker response in mucopolysaccharidosis type I after successful hematopoietic cell transplantation

Background: Residual disease, primarily involving musculoskeletal tissue, is a common problem in patients with neuronopathic mucopolysaccharidosis type I (MPS I, Hurler or severe Hurler-Scheie phenotype) after a successful hematopoietic cell transplantation (HCT). The concentration of the GAG derived biomarkers heparan sulfate (HS) and dermatan sulfate (DS), may reflect residual disease and is used for monitoring biochemical response to therapies. This study investigates the response of HS and DS in blood and urine to HCT in MPS I patients. Methods: In 143 blood- and urine samples of 17 neuronophatic MPS I patients, collected prior and post successful HCT, the concentration of the disaccharides derived after full enzymatic digestion of HS and DS were analyzed by multiplex liquid chromatography tandem-mass spectrometry (LC-MS/MS). Results: Median follow up after HCT was 2.4. years (range 0-11. years). HCT led to a rapid decrease of both HS and DS. However, only 38% of the patients reached normal HS levels in blood and even less patients (6%) reached normal DS levels. In none of the patients normalization of HS or DS was observed in urine. Conclusions: Biomarker response after HCT is incomplete, which may reflect residual disease activity. Novel therapeutic strategies should aim for full metabolic correction to minimize clinical manifestations.