GNPTG encodes the gamma subunit of N-acetylglucosamine-1-phosphotransferase (GlcNAc-1-phosphotransferase), a non-catalytic component essential for lysosomal enzyme trafficking 1. This enzyme complex catalyzes the formation of mannose 6-phosphate (M6P) markers on lysosomal hydrolases in the Golgi apparatus, enabling their proper targeting to lysosomes 2. The gamma subunit binds and presents high mannose glycans to the catalytic alpha/beta subunits encoded by GNPTAB, enhancing the rate of phosphate transfer to acceptor oligosaccharides 1. GNPTG associates with the GlcNAc-1-phosphotransferase complex in the Golgi and is crucial for maintaining enzyme stability 2. Pathogenic variants in GNPTG cause mucolipidosis type III gamma (MLIII gamma), an autosomal recessive lysosomal storage disorder characterized by defective lysosomal enzyme trafficking and cellular accumulation of undegraded macromolecules 34. Unlike GNPTAB mutations that cause more severe phenotypes including impaired bone resorption, GNPTG mutations specifically result in MLIII gamma with distinct clinical features and preserved bone remodeling 5. The protein plays a fundamental role in lysosomal biogenesis and has been identified as a potential therapeutic target in chr16 kidney disease and calcific aortic valve disease 67.