Observational Study to Assess Disease Symptoms and Progression in Participants With Sanfilippo Syndrome Type C (Mucopolysaccharidosis Type III [MPS III] C)

The study will be conducted remotely; no in-person visits are required. Approximately 35 participants with MPS IIIC will be enrolled in the study through a study site in the United States of America (USA). Enrollment of the first 25 participants with age ≤10 years will help ensure that the data collected from these younger participants will provide a better understanding of the early phase of the disease that may be relevant for future drug development. The remaining 10 participants will be between 11 to 25 years of age. The cutoff for the study is 25 years old. Participants speaking either Spanish, Portuguese, German, French or English may enroll in the study.

At Screening (Visit 1), the site coordinator based at UT Southwestern will review the laboratory report with a confirmed diagnosis of Hgsnat-deficiency MPS IIIC and a mutational analysis report demonstrating homozygous or compound heterozygous, pathogenic, and/or potentially pathogenic variants in the Hgsnat gene to assess the eligibility of the participants. After confirming diagnosis by the site coordinator, the caregiver or legal representative(s) will read and sign the informed consent form electronically, and when possible, the participant will provide adult or pediatric assent electronically.

At Baseline (Visit 2), the legal representative(s) or caregiver will be asked to complete electronic demographics and medical record questionnaire via the C-RARE App.

At Baseline (Visit 2) and at 6-month intervals (from Visit 3 through the end of the study), the legal representative(s) or caregiver will be asked to complete questionnaires and record home video assessments using a dedicated study app called C-RARE. Functional and cognitive abilities will be captured in the home environment by video and PEDI-CAT, an electronic a caregiver reported outcome assessment.

The legal representative(s) or caregiver will be provided with a C-RARE kit (via mailing), which includes a manual and props, as well as training for using the app. Baseline at-home visit (demographics, medical/surgical history, concomitant medications/therapy history, video and PEDI-CAT assessment, and ObsRO) should be completed at Visit 2. At-home Visit 3 to Visit 6 (video, PEDI-CAT assessment, and ObsRO) should be completed within a 14-day period for each visit. The legal representative(s) or caregiver will be provided with the timeline for each visit.