⁃ Confirmed diagnosis of Sanfilippo syndrome type C disease by all of the following:

• Deficiency in heparan-alpha-glucosaminide N-acetyltransferase enzyme activity

• Has presented with signs/symptoms consistent with Sanfilippo syndrome type C, or, for individuals who have not presented with signs/symptoms of disease (eg, siblings of known patients), the determination of eligibility will be at the discretion of the Sponsor in conjunction with the site Investigator

• Genomic DNA analysis demonstrating homozygous or compound heterozygous, pathogenic and/or potentially pathogenic variants in the HGSNAT gene

• Accumulated GAG HS in urine

• Written informed consent from parent or legal guardian and assent from patient, if required

• Parent/legal guardian willing to accompany the patient to all study visits

• Ability to comply with protocol requirements, in the opinion of the Investigator

• Negative urine pregnancy test at screening (nonsterile females of childbearing potential only).

⁃ Functional abilities:

• Able to take food or liquid by mouth, able to walk with or without assistance.

• Has an age equivalent on the Vineland Adaptive Behavior Scales (VABS) of ≥1 year.