Abstract

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and their associated (Cas) proteins have transformed from an obscure prokaryotic adaptive immune mechanism into the most versatile toolkit in modern molecular biology. Within little more than a decade of the demonstration that Cas9 could be programmed to cleave defined genomic sequences, the field has progressed to the first regulatory approval of a CRISPR-based medicine and to bespoke, patient-specific therapies delivered directly in the body. This narrative review synthesizes developments from 2019 onward, situated against foundational earlier work, to provide an integrated and critical account of where the technology now stands. We first revisit the biological logic of CRISPR immunity and the structural basis of RNA-guided DNA recognition, because these principles continue to constrain and inspire engineering. We then examine the maturation of precision editing modalities-high-fidelity nucleases, cytosine and adenine base editors, and prime editors-analyzing the mechanistic tradeoffs that govern their efficiency, product purity, and off-target behavior. Parallel advances in transcriptional and epigenetic modulation, RNA-targeting effectors, and CRISPR-based diagnostics are appraised for their distinct value propositions. A recurring theme is the tension between editing potency and specificity, and between the breadth of correctable mutations and the practicality of delivery. We compare conflicting reports on unintended consequences, including large structural rearrangements, activation of the p53 pathway, and editor-dependent off-target mutagenesis, and we weigh their translational implications. Landmark clinical results in haemoglobinopathies, transthyretin amyloidosis, and ultra-rare metabolic disease are evaluated critically, alongside persistent barriers of extrahepatic delivery, immunogenicity, equitable access, and germline governance. We conclude by identifying priority research gaps and plausible near-term directions, arguing that the decisive challenges are now as much translational and ethical as they are molecular.

Keywords: CRISPR-Cas9, Base editing, Prime editing, Genome editing, Gene therapy, Cas13, Off-target effects, Therapeutic delivery