Base Editing (BE4max) for F8 c.5291A>G (p.Gln1764Arg) in Hemophilia A

Base Editing (BE4max) via LNP delivery is a rationale-driven therapeutic strategy for Hemophilia A targeting the F8 c.5291A>G (p.Gln1764Arg) variant (Pathogenic, missense variant). The editing system (BE4max (cytosine base editor)) converts the pathogenic C to T (or G to A on the target strand), restoring the wild-type codon. Target tissue: Liver. Therapeutic goal: Correct loss-of-function F8 mutations in hepatocyte/endothelial lineages at Xq28 to restore >5-10% FVIII activity and convert severe hemophilia A to a mild or asymptomatic phenotype.. Risk profile: off-target Medium (bystander bases in editing window), delivery complexity Low, immunogenicity Low.

1. Molecular basis: F8 NM_000132.4(F8):c.5291A>G (p.Gln1764Arg) is classified as Pathogenic (ClinVar variation ID 1685789). Molecular consequence: missense variant. Protein change: Q1764R. 2. Epidemiology: Hemophilia A is an X-linked congenital bleeding disorder caused by deficiency or dysfunction of coagulation factor VIII and accounts for ~80% of hemophilia cases. Birth prevalence in males is ~24.6 per 100,000, and overall prevalence is ~1 in 5,000 live male births (WEB-01, WEB-11). Severe disease ( 3. Standard of care: Standard care is lifelong replacement or mimetic prophylaxis. Severe patients receive regular intravenous or subcutaneous prophylaxis with plasma-derived or recombinant factor VIII, extended half-life FVIII products, or non-factor agents such as the FVIII-mimetic bispecific antibody emicizumab and r 4. Pipeline: Multiple AAV-F8 gene replacement therapies have reached late-stage development. Giroctocogene fitelparvovec (AAV6-BDD F8) is in Phase 3 (Alta Phase 1/2, AFFINE Phase 3) with RMAT/Fast Track/Orphan designations (WEB-04). Additional AAV-F8 products have achieved regulatory approval in major markets (E 5. CBE clinical validation: BE4max (Koblan et al. 2018) is the gold-standard cytosine base editor. Multiple CBE programs are in clinical development for liver and hematologic targets.

1. No published data specifically correcting F8 c.5291A>G (p.Gln1764Arg) with Base Editing (BE4max); 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.