NIH investigators, for the first time, identified specific mutations associated with stuttering. These mutations are located within the genes encoding three enzymes, Glc-NAc phosphotransferase catalytic subunit [GNPTAB], Glc-NAc phosphotransferase recognition subunit [GNPTG], and N-acetylglucosamine-1-phosphodiester alpha-N-acetylglucosaminidase [NAGPA]. Together these constitute the pathway that targets lysosomal enzymes to their proper location. This pathway is associated with lysosomal storage disorders, and thereby this discovery provides potential novel therapeutic targets for amelioration of stuttering. This discovery has the potential to facilitate DNA-based (micro-array) testing among individuals who stutter, as well as enzyme-replacement therapy and small-molecule chaperone therapy for treatment of stuttering. The mutations described in this invention may account for up to 5-10% of this disorder in individuals who stutter, estimated to represent 60,000-120,000 individuals in the United States.