Enzyme Replacement Therapy in Mucopolysaccharidosis Type VII: A Three-Year Clinical Outcome Study of the First Taiwanese Case

Background and Clinical Significance: Mucopolysaccharidosis type VII (MPS VII), an ultrarare lysosomal storage disorder caused by beta-glucuronidase deficiency, presents significant therapeutic challenges. Given its extreme rarity and limited treatment experience in Asian populations, documenting long-term treatment outcomes is crucial for advancing clinical knowledge and improving patient care. Case Presentation: We report a 3-year follow-up of enzyme replacement therapy (ERT) in the first Taiwanese case of MPS VII. The patient, who initially presented with hydrops fetalis and developmental delay, was diagnosed at age 4 through genetic analysis, which revealed compound heterozygous variants of c.104C > A (p.Ser35Ter) and c.1454C > T (p.Ser485Phe) on the GUSB gene. ERT with vestronidase alfa was initiated at age 6. During the follow-up period, significant clinical improvements were observed, including elimination of oxygen dependency, with BiPAP needed only during sleep; changes in mobility, with 6-min walk test distance showing an initial decline from 130 to 70 m followed by partial recovery to 95 m after multiple orthopedic surgeries; and steady progression of growth parameters showed, with height increasing from 110 to 118 cm. Urinary glycosaminoglycan (GAG) levels measured by dimethylmethylene blue spectrophotometry decreased and stabilized. The patient's cardiac and hepatic conditions remained stable, although splenomegaly persisted. No severe adverse events were reported during ERT. Conclusions: This case demonstrates the effectiveness and safety of long-term ERT in MPS VII, particularly in improving respiratory function and physical performance. Our experience highlights the importance of early diagnosis and treatment initiation, while providing valuable insights into the management of this ultrarare disease in the Asian population.