Long-term observational, non-randomized study of enzyme replacement therapy in late-onset glycogenosis type II

Objectives Type II glycogenosis (GSDII) is a lysosomal storage disorder due to acid alpha-glucosidase (GAA) deficiency. Enzyme replacement therapy (ERT) with human recombinant alpha-glucosidase (rhGAA) has been demonstrated to be effective in the treatment of infantile forms of GSDII, but little information is available concerning late-onset phenotypes. Long-term follow-up studies are not available at present. The aim of this study was to evaluate the ERT long-term effects in late-onset GSDII. Methods Twenty-four patients, including 7 juveniles and 17 adults, received bi-weekly infusion of rhGAA (20 mg/kg) for at least 36 months. Clinical conditions, muscular function (6-min walking test, 6MWT; Walton scale, WS), respiratory function (vital capacity, VC; forced expiratory volume, FEV1; arterial pCO2), and muscle enzymes were assessed every 6 months. Results The 6MWT improved in both juvenile and adult patients (p=0.01, p=0.0002, respectively), as well as in patients with moderate to severe muscle function impairment (WS>3.5; p=0.002). An overall improvement in WS was also observed (p=0.0003). VC and FEV1 remained unchanged, while pCO2 decreased (p=0.017). Muscle enzymes decreased significantly (p<0.0001). Two patients (8%) showed transient secondary events during ERT. Conclusions Long-term ERT with rhGAA was shown to be safe, well tolerated, and effective in improving motor function and in stabilizing respiratory function in lateonset GSDII. The response pattern showed a progressive clinical improvement during the follow-up period in juvenile patients, while in adults it reached and maintained a plateau after the first year of treatment.