The goal of this study is to conduct a randomized, placebo-controlled trial (RCT) of ganaxolone, a neuroactive steroid (NAS), in autistic children and adolescents aged 5 to 17 years old. Ganaxolone is approved and effective for treating seizures in children as young as 2 years old who have CDKL5 deficiency disorder (CDD), a neurogenetic condition associated with developmental delays, seizure disorder, hypotonia, visual impairments, and autistic features. The primary outcome of interest for this trial is irritability on the Aberrant Behavior Checklist (ABC) because it is a common symptom of emotion dysregulation in ASD that impacts quality of life, including mental health, independence, educational opportunities, and integration into the community. The secondary domains of interest for this trial are restricted and repetitive behaviors (RRB), specifically insistence on sameness (IS), a subdomain of RRB characterized by inflexibility and a strong preference for predictable routines and familiar environments. Secondary outcome measures include the IS subscale from the Dimensional Assessment of Repetitive Behaviors (DARB) and subscales of the Clinical Global Impressions Scale for irritability (CGI-IR) and IS (CGI-IS). For participants living within 150 miles of Stanford University, we require participants to attend site visits and attempt EEG and MRI procedures before and after the trial, though we are recruiting nationally and the study can be completed without site vists.