Limited Clinical Impact of Anti-Idursulfase Antibodies Developed During Long-Term Idursulfase Enzyme Replacement Therapy (ERT) in Mucopolysaccharidosis II (MPS II, Hunter Syndrome) Patients Aged 5-35 Years

38% by 240 weeks (n= 5). Forced expiratory volume (FEV1) increased approximately 11% at 96 weeks (n = 33) and was maintained at 240 weeks (n= 5) (3). After 7 years, FVC improved by 47% (n= 5) and FEV1 by 34% (n= 6), showing continued upward trajectories. (2). ERT treatment (96 weeks) showed stable left ventricular function (n= 53) and regression of intraventricular septal hypertrophy (n = 54) in patients with a mean age of 11.8 (± 5.4) years. Cardiac valve disease remained physiologically stable with ERT; mitral valve stenosis/ regurgitation and aortic valve stenosis remained unchanged. Aortic regurgitation increased significantly but level of severity was assessed as mainly trace to mild. (4). Patients starting ERT treatment b 6 yrs had mean improved growth rates as compared to normalizedMPS VI growth curves; the largest improvement seen in patients with the highest uGAG levels who started ERT b 3 yrs, showing a mean additional growth improvement of N10 cm over 5 years. (5) ERT treated patients (n= 77) had a 19.48% mortality rate compared to 60% in untreated patients (n= 10). (6) These data support that galsulfase is relatively safe and demonstrates improvements in long-term clinical outcomes in endurance, respiratory and cardiac functions, aswell as in growth andmortality.