Researchers evaluated CRISPR–Cas3 as an alternative genome‑editing strategy to induce long deletions at the transthyretin (TTR) locus and achieved near‑complete loss of expression in vitro and substantial reductions in vivo. A single lipid nanoparticle dose produced ~48.7% hepatic editing and an ~80% fall in serum TTR in mouse models. Cas3 generated directional deletions up to tens of kilobases with fewer reproducible off‑target mutations than Cas9 in the reported experiments. The work used optimized CRISPR RNAs and demonstrated attenuated macrophage‑associated TTR deposition in humanized mouse models. These results position Cas3 as a distinct tool for therapeutic gene disruption when large deletions are preferable to small indels, with implications for permanent gene‑silencing strategies in ATTR and other protein‑misfolding disorders.