Base Editing (ABE8e) for HBA1/HBA2 c.358C>T (p.Pro120Ser) in Hb Bart's hydrops fetalis (alpha-thalassemia major)

Base Editing (ABE8e) via RNP electroporation (ex vivo) delivery is a rationale-driven therapeutic strategy for Hb Bart's hydrops fetalis (alpha-thalassemia major) targeting the HBA1/HBA2 c.358C>T (p.Pro120Ser) variant (Pathogenic, missense variant). The editing system (ABE8e-nSpCas9 (adenine base editor)) converts the pathogenic A back to G on the target strand, restoring the wild-type codon. Target tissue: Blood/HSC. Therapeutic goal: Restore sufficient alpha-globin expression in fetal/newborn erythroid cells to convert lethal Hb Bart's hydrops fetalis into survivable phenotype or cure transfusion dependence. Risk profile: off-target Medium (bystander bases in editing window), delivery complexity Medium, immunogenicity Low.

1. Molecular basis: HBA1/HBA2 NM_000558.5(HBA1):c.358C>T (p.Pro120Ser) is classified as Pathogenic (ClinVar variation ID 811900). Molecular consequence: missense variant. Protein change: P120S. 2. Epidemiology: Executed all paper-assigned subtasks from plan.jsonl for Hb Bart's hydrops fetalis / alpha-thalassemia major. For severity/urgency (S1-S3, U1-U2), collected cohort and registry data on survival, neurodevelopment, organ damage, healthcare utilization, and chronic transfusion/chelation burden, plus re 3. Standard of care: Executed all web-assigned subtasks from plan.jsonl: (1) disease definition/natural history and patient journey; (2) urgency U1–U3 including current standard of care, access, and epidemiology; (3) therapeutic landscape across modalities and clinical development status; (4) regulatory and safety persp 4. Pipeline: Orphanet and linked rare disease resources classify hemoglobin Bart’s hydrops fetalis (alpha-thalassemia major) as a severe, typically lethal perinatal disorder caused by deletion or inactivation of all four alpha-globin genes. Clinical course is marked by fetal hydrops, severe anemia, cardiomegaly, 5. ABE clinical validation: ABE8e (Richter et al. 2020, Nat Biotechnol) achieves ~1.7x higher editing efficiency than ABE7.10. VERVE-101 demonstrated first-in-human LNP-ABE liver editing with 55-66% PCSK9 reduction (Raal et al. 2025, NEJM). Beam Therapeutics is advancing multiple ABE programs.

1. No published data specifically correcting HBA1/HBA2 c.358C>T (p.Pro120Ser) with Base Editing (ABE8e); strategy is based on general principles and must be validated preclinically.
2. PAM availability and bystander base analysis for the specific genomic context have not been performed. If no canonical NGG PAM positions the target within the editing window, PAM-flexible variants (SpRY) may be needed.
3. Long-term durability, off-target genome-wide effects, and immunogenicity in the target patient population require thorough preclinical and clinical evaluation.