Inclusion Criteria: 1. Age 18 - 80 years old (including the critical values), regardless of gender; 2. Body weight at the time of screening is between 40 - 90kg (including the critical values); 3. TTR gene mutation is confirmed by genetic testing; 4. At the time of screening, the following laboratory standards must be met: 1. AST, ALT, and TBIL ≤ the upper limit of the normal value (ULN); 2. For subjects with Gilbert syndrome, TBIL ≤ 2 times ULN; 3. Glomerular filtration rate (GFR) ≥ 45 mL/min/1.73m2 (calculated according to the CKD-EPI formula); 4. Platelet count ≥ 100 × 109/L; 5. Partial thromboplastin time (APTT), prothrombin time (PT), and thrombin generation time (TGT) are all within the reference value range, fibrinogen (FIB) ≥ the lower limit of the normal value (LLN) and ≤ 1.5\*ULN, the international normalized ratio (INR) ≤ ULN, and if taking anticoagulant drugs, it is ≤ 2.5\*ULN; 6. Vitamin A and vitamin B12 ≥ the lower limit of the reference value (LLN); 7. Low-density lipoprotein cholesterol (LDL) \< 200 mg/dL (5.17 mmol/L). 5. Drugs approved for the treatment of ATTR are not accessible (Criterion A) and/or the disease still progresses despite the use of drugs approved for the treatment of ATTR (Criterion B): * Criterion A: Meeting one or more of the following criteria: 1. Drugs for the treatment of ATTR are not marketed in China; 2. Unable to receive the approved drugs for ATTR treatment (e.g., intolerance or other medical, cost and/or other reasons); * Criterion B: Subjects have received ATTR drug treatment for at least 3 months, but the subject's condition has progressed as assessed by the investigator, and meets any of the following criteria: ATTR-CM: a. Increased number of hospitalizations related to heart failure; b. Worsening of NYHA classification; c. Decrease in KCCQ score by at least 5 points; d. Decrease in 6-MWT by at least 30m; e. Increase in NT-proBNP by 30%; f. Increase in Troponin I by 30%; g. Echocardiography indicates an increase in left ventricular wall thickness by 2mm; h. Echocardiography indicates a decrease in left ventricular ejection fraction by ≥ 5% or a decrease in global longitudinal strain by ≥ 1% or a decrease in stroke volume by ≥ 5%; i. New conduction block appears; ATTR-PN: a. PND score increase by ≥ 1 point; b. FAP increases by 1 stage; c. NIS score increase by ≥ 5 points; d. NIS-Lower Limb score increase by ≥ 5 points; e. mBMI decrease by ≥ 25 kg/m2×g/L; f. 10-MWT decrease by ≥ 0.1 m/s; g. Electroneurophysiological examination (electromyography) worsens compared to the previous. 6. Agree to stop drinking alcohol within the screening period to 28 days after administration; 7. Female subjects need to be menopausal (absence of menstruation for at least 1 year) or have undergone uterine/ovarian resection surgery; Male subjects and their partners have no fertility plans from the screening period to 6 months after the end of the trial and agree to take effective non-pharmaceutical contraceptive measures during the trial; 8. The subject himself/herself (or his/her legally recognized representative) understands and signs the informed consent form; 9. Agree not to receive other ATTR drug intervention treatment within at least 8 weeks after administration of YOLT-201; For ATTR-PN only: 10. Diagnosed as ATTR-PN according to the "Consensus on the Diagnosis and Treatment of Transthyretin Amyloidosis Polyneuropathy", and the NIS score at the screening is ≥ 5 and ≤ 130, and the PND score is ≤ IIIb; 11. NT-proBNP \< 600pg/ml at the screening; For ATTR-CM only: 12. Diagnosed as ATTR-CM according to the "Expert Consensus on the Diagnosis and Treatment of Transthyretin Cardiac Amyloidosis"; 13. The New York Heart Association (NYHA) cardiac function classification is grade II - III; 14. The 6-minute walk test (6-MWT) is ≥ 150 m at the screening; 15. NT-proBNP is ≥ 600pg/mL and ≤ 3000pg/mL at the screening; 16. At the screening, echocardiography suggests evidence of cardiac involvement: the thickness of the interventricular septum and/or the posterior wall of the left ventricle is ≥ 12 mm. Exclusion Criteria: 1. Amyloidosis is not caused by TTR protein, such as light chain amyloidosis; 2. There is meningeal transthyretin amyloidosis; 3. Allergic to any lipid nanoparticle (LNP) component or has previously received LNP and experienced treatment-related laboratory abnormalities or adverse events; 4. Use any of the following ATTR treatments within the prescribed time: * In the dose escalation stage of the first stage, the use history of Patisiran, Inotersen, and Vutrisiran is excluded; * In the dose expansion stage of the second stage, the following are excluded: Patisiran is used within 90 days before the administration of the investigational drug; Inotersen is used within 160 days before the administration of the investigational drug; Vutrisiran has a previous use history; * Tafamidis: used within 10 days before the administration of the investigational drug; * Diflunisal: used within 3 days before the administration of the investigational drug; * Doxycycline and/or taurodeoxycholic acid: used within 14 days before the administration of the investigational drug; * Previous use history of investigational gene editing drugs; * Other drugs for the treatment of ATTR: the last use is less than 30 days or 5 half-lives before the administration of the investigational drug, whichever is longer. 5. Unable or unwilling to supplement vitamin A during the trial; 6. History of multiple myeloma; 7. Ophthalmological examination results at the screening are consistent with vitamin A deficiency; 8. Abnormal thyroid function test with clinical significance judged by the investigator; 9. Known or suspected systemic infection (viral, parasitic or fungal infection) within 14 days before screening; 10. History of past hepatitis B virus, hepatitis C virus, acquired immunodeficiency syndrome or positive HBsAg, HCV-Ab, and HIV-Ab at the screening; 11. History of previous liver, heart or other organ transplantation or bone marrow transplantation or expected transplantation within 1 year (except for the history of corneal transplantation or planned corneal transplantation); 12. History of bleeding or coagulation disorders (such as cirrhosis, malignant hematological disease, antiphospholipid antibody syndrome); 13. History of acute thrombosis within 6 months before screening (such as acute myocardial infarction, acute cerebral infarction), or positive Leiden factor V and/or prothrombin gene test; 14. History of malignant tumor within 5 years before screening (except for basal cell carcinoma of the skin, radicalized squamous cell carcinoma of the skin, and carcinoma in situ of the cervix); 15. Planned invasive cardiovascular surgery during the trial (such as coronary artery stent/coronary artery bypass, pacemaker placement, etc.); those who have undergone cardiovascular invasive surgery within 90 days before screening or have been hospitalized due to heart failure; 16. History of alcohol abuse within 3 years before screening (definition of alcohol abuse: women drink ≥ 4 glasses/day or 8 glasses/week, men ≥ 5 glasses or 15 glasses/week, where 1 glass = 14g of pure alcohol); 17. Expected survival period is less than 1 year; 18. Other situations that the investigator deems inappropriate to enter this trial; For ATTR-PN only: 19. Other known diseases that cause motor or sensory neuropathy (such as diabetic neuropathy, neuropathy related to autoimmune diseases, etc.); 20. Diagnosed with type 1 diabetes or type 2 diabetes for ≥ 5 years; 21. NYHA cardiac function classification is grade III or IV within 90 days before screening; For ATTR-CM only: 22. NYHA cardiac function classification is grade IV within 90 days before screening; 23. PND score is grade IIIa, IIIb or IV at the screening; 24. Suffering from other cardiomyopathies not caused by TTR (such as hypertensive cardiomyopathy, valvular heart disease, cardiomyopathy caused by ischemic heart disease, etc.).