Lysosomal acetyltransferase that acetylates the non- reducing terminal alpha-glucosamine residue of intralysosomal heparin or heparan sulfate, converting it into a substrate for luminal alpha-N-acetyl glucosaminidase. Defects in HGSNAT are the cause of mucopolysaccharidosis type 3C (MPS3C); also known as Sanfilippo C syndrome. MPS3C is a form of mucopolysaccharidosis type 3, an autosomal recessive lysosomal storage disease due to impaired degradation of heparan sulfate. MPS3 is characterized by severe central nervous system degeneration, but only mild somatic disease. Onset of clinical features usually occurs between 2 and 6 years; severe neurologic degeneration occurs in most patients between 6 and 10 years of age, and death occurs typically during the second or third decade of life. 2 isoforms of the human protein are produced by alternative initiation. Note: This description may include information from UniProtKB.