CS-121 APOC3 Base Editing in Children and Adolescents With Hyperchylomicronemia

Inclusion Criteria: * Male or female participants aged 4 years ≤ age \< 18 years. * Severe hypertriglyceridemia (sHTG), defined as a triglyceride (TG) level ≥ 500 mg/dL. * Confirmed diagnosis of genetically inherited FCS via genetic testing, or clinically diagnosed FCS plus persistent chylomicronemia. * Failure to achieve adequate TG control, For participants under 8 years of age, the investigator determine at their discretion whether prior lipidlowering therapy has been administered. * Participants aged 6 years and above must sign the informed consent form themselves; for participants under 18 years of age, their parent/legal guardian must sign the informed consent form. (Participants under 6 years of age are exempt from signing the written informed consent form). * Female participants of childbearing potential must have a negative result on serum pregnancy testing. Exclusion Criteria: * Currently participating in other interventional clinical studies, or having an insufficient washout period of less than 5 half-lives or 30 days (whichever is longer) since the last administration of other investigational drugs. * Used antisense oligonucleotide (ASO)-based or small interfering RNA (siRNA)-based lipid-lowering drugs targeting APOC3 within 3 months prior to study drug administration. * History of acute pancreatitis within 1 month before dosing. * Patients who underwent major surgery within 3 months prior to study drug administration and are judged by the investigator as unsu…