(A) Seropositivity, as defined as ≥1:20, in the pediatric MMA cohort compared with historical controls. There was a lower-than-expected AAV2 (p = 0.0066) and AAV8 (p = 0.0408) NAb seroprevalance in MMA individuals ≤18 years. (B) Neutralizing antibody prevalence to AAV serotypes 2, 8, and 9 by age. The seroprevalance of AAV2, AAV8, and AAV9 NAbs between children and adults was significantly different for all serotypes with a higher incidence of seropositivity in adults (7/11). *p < 0.05, **p < 0.01, ***p < 0.001.