Also, while the potential therapeutic advantage of above-normal enzyme expression in donor cells has been demonstrated for HSC gene therapy in MLD [8], MPS I [65], and GLD mouse models [66], in this study Twi mice transplanted with GALC-overexpressing NSC did not show a significant amelioration in terms of survival as compared with Twi mice transplanted with NSC expressing physiological enzyme levels. The gene discussed is GALC; the disease is metachromatic leukodystrophy.