30 months follow-up of an early enzyme replacement therapy in a severe Morquio A patient: About one case

Patients under 5years were not evaluated in the phase-3 study for enzyme replacement therapy (ERT) in MPS IV A. Here we describe the evolution of a severe Morquio A pediatric patient who was diagnosed at 19months old and treated by ERT at 21months old for the next 30months. Applying the standard ERT protocol on this very young patient appeared to reduce his urinary excretion of glycosaminoglycans (GAGs); the improvements in both the 6minute-walk test (6MWT) and the stair climb test, however, were no different than those reported in the nature history study. Additionally, this young patient experienced many ERT-associated side effects, and as a result a specific corticosteroid protocol (1mg/kg of betamethasone the day before and 1h before the ERT infusion) was given to avoid adverse events. Under these treatments, the height of this patient increased during the first year of the ERT although no more height gain was observed thereafter for 18months. However, despite of ERT, his bone deformities (including severe pectus carinatum) actually worsened and his medullar cervical spine compression showed no improvement (thus needed decompression surgery). Conclusion: early ERT treatment did not improve the bone outcome in this severe MPS IV A patient after the 30months-long treatment. A longer term follow up is required to further assess the efficacy of ERT on both the motor and the respiratory function of the patient.