Autologous Hematopoietic Stem Cell Transplantation for Neurological Damage Associated With Hereditary Homocysteine Remethylation Disorders

Inclusion Criteria: 1. Aged 18 to 55 years, regardless of gender. 2. Comprehensive clinical, biochemical, and genetic diagnosis of hereditary homocysteine remethylation disorders. 3. Evidence of neurological involvement, including but not limited to gait disturbance, balance impairment, cognitive dysfunction, cerebral white matter lesions. 4. Prior standardized metabolic therapy (folic acid, vitamin B12, betaine) with suboptimal clinical response. 5. Persistent severe metabolic abnormality, i.e., sustained elevated homocysteine (\>50 umol/L). 6. Multidisciplinary consensus confirming lack of effective alternative therapies and ongoing risk of disease progression. 7. Voluntary participation, signed informed consent, adequate treatment adherence, and willingness to complete follow-up assessments. Exclusion Criteria: 1. Prior hematopoietic stem cell transplantation or other cell transplantation. 2. Severe dysfunction of critical organs (heart, lung, liver, kidney) deemed incompatible with study treatment by investigators. 3. Active, uncontrolled infection. 4. Active tuberculosis, hepatitis B, hepatitis C, HIV infection, or other infectious diseases judged inappropriate for enrollment by investigators. 5. Active malignancy or prior malignant history that may confound safety and efficacy evaluations. 6. Severe underlying comorbidities likely to interfere with study treatment or outcome assessment. 7. Severe psychiatric disorder or cognitive impairment with poor adherence precluding completion of treatment and follow-up. 8. Pregnant or lactating females, or participants unwilling to use effective contraception throughout the study period. 9. Severe hypersensitivity to any study-related medication or intervention. 10. Participation in other interventional clinical trials within the past 4 weeks or ongoing observation period of another clinical trial. 11. No documented disease progression within the preceding 12 months. 12. Minimal neurological symptoms with no meaningful impact on activities of daily living and low short-term progression risk per investigator assessment. 13. Established standard therapies proven to alter natural disease history with stable disease and satisfactory therapeutic response. 14. End-stage disease with extensive irreversible neurological impairment (severe motor/cognitive failure or multi-organ dysfunction) with minimal expected therapeutic benefit. 15. Any other conditions deemed unsuitable for study participation by investigators.