A self-inactivating HIV-based lentivirus vector expressing the human arylsulfatase A ARSA gene was used in a pre-clinical study in metachromatic leukodystrophy [259]: 10-month-old knock-out mice received unilateral injection into the right fimbria in the hippocampus under stereotactic guidance and were examined one, three and five months later. The gene discussed is ARSA; the disease is metachromatic leukodystrophy.