Natural History Study of Participants With Sanfilippo Syndrome Type IIIC

This is a multi-center, natural history study of subjects with Sanfilippo syndrome type C or MPS IIIC. This study will combine a retrospective review of medical records and an ongoing collection of clinical data on an observational basis. Real-world data will be collected at home using a recording device.

Participants will be asked to attend clinic visits in person on a yearly basis. In clinic visits will include neurocognitive, developmental, behavioral, biochemical, imaging measures as well as retrospective medical record analysis.

At 6-month intervals between clinic visits, participants will be contacted remotely for some safety assessments (e.g., collecting information about concomitant medications, concurrent illnesses, and procedure-related adverse events [AEs] and serious AEs [SAEs] since last clinic visit).

At 6-month intervals, caregivers will complete questionnaires and record home video assessments using a dedicated, compliant study application (app) called C-RARE (Recording Application for Real-World Evidence). The C-RARE app consists of 9 tasks of Activities of Daily Living and socialization as well as three parent reported Sanfilippo specific questionnaires.

The objectives of this study are:

• To enhance the understanding of the natural history and progression of MPS IIIC syndrome on behavior, cognitive abilities, mobility, vision, hearing, speech, and expressive and receptive language
• To define and categorize clinical endpoints that may be used in future clinical trials

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