RPE65-associated Leber congenital amaurosis (RPE65-LCA)

Voretigene neparvovec (Luxturna, Spark Therapeutics) is the first FDA-approved (December 2017) gene therapy for an inherited retinal dystrophy. It delivers functional RPE65 via AAV2 subretinal injection and is applicable to patients with biallelic RPE65 mutations including splice-site variants like c.11+5G>A, provided sufficient viable retinal cells remain. This approval established a regulatory and clinical paradigm for retinal gene therapies.

The pivotal Phase III trial (NCT00999609) demonstrated statistically significant improvement in multi-luminance mobility testing (MLMT) at one year in 21 treated vs 10 control eyes (Russell et al., Lancet 2017; PMID: 28712537). Full-field stimulus testing (FST) showed ~100-fold improvement in light sensitivity. Long-term follow-up data from Phase I patients (Maguire et al., 2019; PMID: 31189025) showed durability of functional vision improvement at 3-4 years post-injection in the originally treated eye. The c.11+5G>A variant disrupts the canonical splice donor site of exon 1, leading to aberrant splicing and loss of functional RPE65 protein, consistent with the loss-of-function mechanism that voretigene neparvovec addresses by providing a functional gene copy.

Long-term follow-up beyond 7-10 years has shown some decline in efficacy in certain patients, suggesting the AAV2-delivered transgene expression may wane over time (Jacobson et al., Ophthalmology 2015; PMID: 25444347). Re-dosing the same eye is complicated by anti-AAV2 neutralizing antibodies, though contralateral eye injection appears feasible. The therapy requires viable retinal photoreceptor cells, so patients with advanced degeneration may not benefit. Cost remains a significant barrier (~$425,000 per eye at US list price). Additionally, subretinal injection carries procedural risks including retinal detachment.

Base Editing (ABE8e) via AAV delivery is a rationale-driven therapeutic strategy for RPE65-associated Leber congenital amaurosis (RPE65-LCA) targeting the RPE65 c.11+5G>A variant (Pathogenic, intron 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: Eye/Retina. Therapeutic goal: Correct or functionally replace biallelic loss-of-function RPE65 variants in retinal pigment epithelium to restore the visual cycle and improve vision.. Risk profile: off-target Medium (bystander bases in editing window), delivery complexity Medium, immunogenicity High (AAV pre-existing immunity).

1. Molecular basis: RPE65 NM_000329.3(RPE65):c.11+5G>A is classified as Pathogenic (ClinVar variation ID 98825). Molecular consequence: intron variant. 2. Epidemiology: RPE65-LCA is an ultra-rare autosomal recessive inherited retinal dystrophy causing severe early-onset vision loss and progressive retinal degeneration; inherited retinal diseases overall affect about 1 in 4000 people with substantial national economic burden. 3. Standard of care: Historically, management was limited to supportive and low-vision care. Luxturna (voretigene neparvovec), an AAV2-based subretinal RPE65 gene augmentation therapy, is now approved for patients with confirmed biallelic RPE65 mutations and viable retinal cells but is costly and access-limited. 4. Pipeline: Luxturna is approved with Phase I/III data; additional ocular gene therapies (e.g., RPGR, ABCA4, ND4) and the in vivo CRISPR therapy EDIT-101 for CEP290-LCA10 illustrate a rapidly evolving pipeline relevant to future RPE65-targeted gene-editing approaches. 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 RPE65 c.11+5G>A 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.