The primary aim is to characterize the PK of IV laronidase in individuals with MPS IH and identify patient specific covariates that impact drug exposure. The secondary aim is to identify key differences pre-and post-HCT leading to variability in PK parameters for patients receiving IV laronidase therapy for the treatment of MPS-IH.

To identify key differences leading to variability in PK parameters for patients receiving IV laronidase therapy for the treatment of MPS-IH. There will be 12 samples per patient (6 pre-transplant and 6-post-transplant). Laronidase will be administered IV per protocol using standard dosing (0.58 mg/kg intravenously on a weekly basis), and six (n=6) blood samples will be collected over 24 hours for the determination of mononuclear cell lysates and plasma laronidase concentrations for a total of 18mL. The second PK monitoring will be obtained using the same PK design but following complete or near-completedonor derived myeloid engraftment which is evaluated at different time pointspost-HCT (day 30, day 42, day 60). The standard is to continue ERT through 8 weeks post-transplant.

Measure indicators for body size and maturation contribute to variability in laronidase exposure in patients with MPS IH.

Measure endogenous source of enzyme present in relation to the transplanted cells.