A Study to Evaluate the SYH2053 Injection in Patients With Heterozygous Familial Hypercholesterolemia (HeFH)

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. \-