The present invention provides means and strategies for treating the lysosomal storage disorder alpha-mannosidosis by enzyme replacement therapy. In particular, the invention pertains to the reduction of stored neutral mannose-rich oligosaccharides in cells within the central nervous system. Accordingly, the present invention provides the use of a lysosomal alpha-mannosidase for the preparation of a medicament for reducing the intracellular levels of neutral mannose-rich oligosaccharides in cells within one or more regions of the central nervous system. The invention further provides a formulation of lysosomal alpha-mannosidase for use as a medicament for reducing the intracellular levels of neutral mannose-rich oligosaccharides in cells within one or more regions of the central nervous system. Also, the invention provides a method of reducing the intracellular levels of neutral mannose-rich oligosaccharides in cells within one or more regions of the central nervous system of a subject, said method comprising administering to said subject a preparation of lysosomal alpha-mannosidase. Finally, the invention pertains to methods of producing, isolating, and purifying an alpha-mannosidase as well as the use of an alpha-mannosidase, which is obtainable according to these methods.
