The present invention pertains to a novel treatment of pathologies caused by an increased synthesis or accumulation of sulfolipids such as sulfatide. The invention provides mutated arylsulfatase A (ARSA or ASA, EC 3.1.6.8) enzymes with increased activity towards sulfatide metabolization. The invention provides nucleic acids encoding the mutant ARSA, the use of the proteins and nucleic acids, as well as pharmaceutical compositions comprising them, in the treatment of lysosomal storage disorders (LSDs) such as metachromatic leukodystrophy (MLD).