Correcting photoreceptor diseases at their source: CRISPR strategies for cone-rod dystrophy and achromatopsia.

BACKGROUND

Cone-rod dystrophy (CORD) and achromatopsia (ACHM) are inherited retinal dystrophies for which conventional adeno-associated virus (AAV) gene augmentation has important limitations, particularly in autosomal-dominant gain-of-function CORD and recessive ACHM. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) offers the potential for one-time, mutation-specific gene correction or allele ablation. This systematic review summarizes preclinical evidence on CRISPR/Cas9-based approaches for CORD and ACHM, focusing on editing efficiency, phenotypic rescue, and safety.

METHODS

This review followed PRISMA guidelines. PubMed, Google Scholar, and ScienceDirect were searched through June 2025 for original experimental studies using CRISPR/Cas9 in CORD or ACHM animal models or human-derived cell lines. Dual independent screening and data extraction were performed. Outcomes related to editing efficiency, structural or functional rescue, and safety were synthesized narratively.

RESULTS

Four studies were included: three targeting CORD and one targeting ACHM. In vivo studies used AAV-delivered SaCas9 to disrupt GUCY2D (or murine orthologs) in mouse and macaque photoreceptors, achieving approximately 8-45% on-target editing in mice and approximately 13% in macaques. Although ablation alone reduced retGC1 expression, it did not improve retinal function; however, a dual-AAV "ablate-and-replace" strategy preserved outer nuclear layer thickness for up to 24 weeks in CORD6 mice. In vitro, PROM1 correction in patient-derived iPSCs restored CD133 expression, and SpCas9-HiFi-mediated PDE6C correction in ACHM iPSCs achieved approximately 80% editing efficiency while preserving pluripotency and showing no detectable off-target effects. Safety data were limited, with immune responses assessed in only one primate study.

CONCLUSIONS

CRISPR/Cas9 shows promising preclinical efficacy for CORD and ACHM, particularly allele-specific ablate-and-replace strategies for CORD and precise HDR-based correction for ACHM. However, the available evidence remains limited, underscoring the need for expanded safety assessment, non-human primate studies, and standardized functional outcomes measures before clinical translation.