CLN2 disease is caused by inherited mutations in the lysosomal protease tripeptidyl peptidase 1 (TPP1). Theoretically this disorder is treatable by both enzyme replacement therapy (ERT) or gene therapy to provide the missing TPP1 enzyme. Both approaches depend on the binding of phosphorylated residues on TPP1 to the mannose-6-phosphate (M6P) receptor expressed on the surface of cells and subsequent trafficking to the lysosome. This phosphorylation not only effectively tags enzymes that will be delivered to the lysosome, but also provides the uptake mechanism for exogenously supplied enzyme. Recently, a variant of GlcNAc-1-phosphotransferase (S1S3) has been generated, which can enhance the M6P content of lysosomal enzymes achieving a much higher level of both mono- and bis-phosphorylation. Our data reveal the resulting hyperphosphorylated lysosomal enzymes have a much higher affinity for the M6P receptor and result in enhanced uptake of lysosomal enzymes into cells. We have applied this hyperphosphorylation strategy to both ERT and gene therapy approaches in CLN2 mice (Tpp1R207X/R207X). For ERT we have intracerebroventricularly (ICV) delivered of either S1S3 hyperphosphorylated recombinant human TPP1 or native rhTPP1. In the modified gene therapy strategy, we have tested neonatal ICV delivery of an AAV9 vector that expresses both TPP1 and the S1S3 phosphotransferase, that results in expression of both enzymes in transduced cells. We have used well established gait and neuropathological outcome measures in addition to survival analyses. These analyses are ongoing, but data so far reveal increased spread of hyperphosphorylated enzyme within the brain parenchyma, and treatment effects of both strategies.