The level of SGSH expression is likely to strongly influence the degree of MPSIIIA disease correction, given that standard allogeneic stem cell transplant with wild-type SGSH expression is ineffective in correcting the clinical phenotype in both MPSIIIA animal models and patients.25, 26, 27 We therefore evaluated the appropriate SGSH LV MOI required to achieve efficacy in human CD34+ cells without adverse toxicity. The gene discussed is CD34; the disease is mucopolysaccharidosis type 3A.