Two-year follow-up after drug desensitization in mucopolysaccharidosis

Background: Mucopolysaccharidosis (MPS) type 1 S and type 2 are rare lysosomal storage disorders characterized by impaired enzyme production, resulting in glycosaminoglycans accumulation within lysosomes. Enzyme Replacement Therapy (ERT) with laronidase and idursulfase are first line treatments, respectively. However, infusion-related hypersensitivity reactions (HR) may lead to ERT discontinuation. Thus, desensitization can be performed to restore ERT. Methods: We report on a two-year follow-up after a combined desensitization approach in two MPS patients experiencing HR to ERT. This approach consists of intravenous rapid desensitization combined with the subcutaneous allergen immunotherapy-like desensitization with the culprit recombinant enzyme. Results: The first patient, suffering from MPS type I, underwent to the combined desensitization approach, and subsequently tolerated weekly standard laronidase infusions for 13 months when HR occurred again. Then, a monthly omalizumab (anti-IgE monoclonal antibody) administration was implemented allowing the patient to restore ERT. The second patient, diagnosed with MPS type 2, was subjected to a similar combined desensitization strategy with idursulfase, and achieved a total desensitization after one year, confirmed by negative skin tests. Thus, he continued standard ERT infusions without HR occurrence. Conclusion: The combined desensitization approach proved effective in conferring immunotolerance for at least one year in both MPS patients, also demonstrated by the negative skin tests in one patient. However, when immunotolerance to ERT is lost, omalizumab administration can be a valid option in restoring ERT.