Study of Cannabidiol in Sanfilippo Syndrome

The goal of this clinical trial is to test cannabidiol in Sanfilippo syndrome. The main questions it aims to answer are: 1) determine the safety of cannabidiol in Sanfilippo syndrome, and 2) explore the efficacy of cannabidiol in treating the neurobehavioral symptoms and functional outcomes of Sanfilippo syndrome. Each participant's caregiver will be asked to complete surveys related to the participant's behavior, mood, sleep, stooling, pain, and caregiver stress intermittently throughout the study. All participants will be enrolled into one of two cohorts based on enrollment order: 1. Sentinel Safety Cohort (first 5 participants) - all participants treated with Epidiolex (cannabidiol) 2. Controlled Cohort (next 30 participants) - participants randomized 1:1 (equal chance) to start treatment with Epidiolex (cannabidiol) or placebo for 16 weeks, followed by an 8-week washout period (no treatment). Participants then switch to the opposite treatment group for 16 weeks followed by all participants treated for 52 weeks with Epidiolex (cannabidiol).