Natural History Study of Participants With Sanfilippo Syndrome Type IIIC

Inclusion Criteria:

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.

Exclusion Criteria:

Patients who meet any of the following criteria will not be eligible to participate in the study:

* Have received an investigational drug within 30 days prior to the Baseline Visit
* Concomitant illness or medical condition or extenuating circumstance that, in the opinion of the Investigator, might compromise the patient's ability to comply with protocol requirements, the patient's well-being or safety, or the interpretability of the patient's clinical data
* The presence of significant non-MPS IIIC-related CNS impairment or behavioral disturbances that would confound the scientific rigor or interpretation of results of the study