IL2RG and Krabbe disease: To confirm that GALC NSCs were overexpressing functional enzyme, we performed an in vitro GALC enzyme assay that was validated by comparing GALC knockout Krabbe disease fibroblasts (Figure S6C, related to Figure 4) with GALC K562 cells that were generated by knocking UbC-GALC-T2A-GFP into the IL2RG locus (Figure S6D, related to Figure 4).