Substrate reduction therapy offers an approach to treatment of certain metabolic disorders, especially glycogen storage diseases and lysosomal storage disorders. In a storage disorder, a critical failure in a metabolic pathway prevents cellular breakdown and disposal of some large molecule. If residual breakdown through other pathways is insufficient to prevent harmful accumulation, the molecule accumulates in the cell and eventually interferes with normal biological processes. Examples of lysosomal storage disorders include Gaucher's disease, Tay-Sachs disease, and Sandhoff disease.
In a metabolic or genetic pathway, enzymes catalyze a series of reactions. Each enzyme is regulated or mediated by one gene through its RNA and protein products. At each phase in the pathway, enzyme activity catalyzes a reaction in which a precursor molecule (the substrate) is transformed into its next intermediate state. Failure of the metabolic pathway leads to accumulation of the substrate, with possible harmful effects. Substrate reduction therapy addresses this failure by reducing the level of the substrate to a point where residual degradative activity is sufficient to prevent substrate accumulation.