Heterozygous Familial Hypercholesterolemia (HeFH) is an autosomal dominant disorder characterized by markedly elevated low-density lipoprotein cholesterol (LDL-C) and increased risk of atherosclerotic cardiovascular disease (ASCVD). This trial aims to evaluate the SYH2053 Injection in patients with HeFH.

This is a multicenter, randomized, double-blind, placebo-controlled Phase III clinical trial conducted in patients with heterozygous familial hypercholesterolemia.

It aims to evaluate the efficacy, safety, and immunogenicity of SYH2053 Injection when administered on the basis of background lipid-lowering therapy and a low-fat diet. The study consists of a screening period and a treatment period.

Inclusion Criteria:

1. Male or female participants ≥18 years of age.
2. HeFH.
3. Stable moderate-to-high intensity statin therapy (± cholesterol absorption inhibitors) .
4. Maintained a low-fat diet for ≥4 weeks before signing the ICF.
5. Fasting LDL-C at screening ≥ 2.6 mmol/L or ≥ 1.4 mmol/L without ASCVD or with ASCVD.
6. Fasting TG ≤5.6 mmol/L at screening.

Exclusion Criteria:

1. HoFH or suspected HoFH.
2. Use of medications that significantly affect LDL-C levels.
3. Hypersensitivity or suspected allergy to oligonucleotide drugs or excipients of the investigational product.
4. Major adverse cardiovascular events (MACE) within 180 days before signing the ICF; history of hemorrhagic stroke; or extreme-risk ASCVD at screening.
5. Uncontrolled (by medication/ablation) or severe arrhythmias within 180 days before signing the ICF.
6. NYHA Class III-IV heart failure or LVEF <40% within 1 year before signing ICF or at screening.
7. Type 1 diabetes.
8. Uncontrolled severe illness or conditions that may interfere with study results/increase risk at screening, according to investigator's judgment.
9. History of malignancy or underlying malignancy within 5 years before signing ICF or at screening.
10. Major surgery within 180 days before signing ICF or planned during the study.
11. History of drug/alcohol abuse within 5 years before signing ICF.
12. Participation in another clinical trial within 90 days or 5 half-lives (whichever is longer) before signing ICF, or planned during the study.
13. Any of the following at screening:

1）SBP ≥160 mmHg or DBP ≥100 mmHg. 2）ALT/AST >3× ULN, or total bilirubin >1.5× ULN. 3）CK >2.5× ULN. 4）QTcF interval: >450 ms for male, >470 ms for female. 5）eGFR <30 mL/min/1.73 m². 6）HBsAg positive with HBV DNA positive; or HCV/syphilis/HIV antibody positive. 7）TSH<LLN, or TSH>ULN. 8）HbA1c >8.5%. 14.Pregnancy/lactation or planned parenthood, and/or without effective contraception for female and male participants of childbearing potential from the study to 3 months after the end of treatment.

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