CRISPR-Cas3: A safer gene-editing tool shows promise for transthyretin amyloidosis treatment

Genetic disorders occur due to alterations in the primary genetic material, deoxyribonucleic acid (DNA), of an organism. Transthyretin amyloidosis (ATTR) is a progressive disorder involving amyloid deposits of misfolded transthyretin (TTR) proteins. The deposits, mainly affecting the heart and the nerves, can lead to symptoms like heart failure and neuropathy. While one of its two major forms is associated with age, the other one is hereditary, resulting from destabilizing mutations in the TTR gene. The therapeutic efficacy of suppressing TTR production has been clearly demonstrated. Although ribonucleic acid (RNA) interference-based drugs can reduce TTR production, they require long-term administration and do not provide a curative treatment.

In recent times, several gene-editing strategies are being utilized to precisely alter the DNA, correcting the mutations or deleting the harmful genetic sequences. These approaches offer enhanced precision and can completely cure genetic disorders. Clustered regularly interspaced short palindromic repeats (CRISPR) refer to the small fragments of viral DNA that are stored by the bacteria as a part of their defense mechanism. CRISPR–Cas9 is a revolutionary gene-editing tool, adapted from this bacterial immune system, that has been widely explored for its clinical applications in recent times.

While the CRISPR–Cas9 shows promising results in developing revolutionary therapies, it has certain limitations, including unintended DNA cuts. Recently, a group of scientists from Japan, led by Professor Tomoji Mashimo and Dr. Saeko Ishida from the Institute of Medical Science, The University of Tokyo, Japan, evaluated the efficacy of the CRISPR–Cas3 system in safely achieving a permanent reduction of TTR production through genome editing of the TTR gene. "Genome editing holds the unique potential to correct the inherited disease-associated genetic abnormalities. We wanted to see if the CRISPR–Cas3 system can be developed as an efficient therapeutic genome-editing tool," mentions Prof. Mashimo, while talking about his motivation behind the study. The article was published in the Nature Biotechnology journal on January 05, 2026.

The CRISPR–Cas3 system has fundamental structural and functional differences when compared to the CRISPR–Cas9 system. In CRISPR–Cas9, a small fragment of RNA, another genetic material, is used as a guide. This guide RNA (gRNA) binds to the target DNA sequence, and the Cas9 protein bound to the gRNA, acts like a molecular scissor and cuts the DNA. However, a multiprotein cascade complex is involved in the CRISPR–Cas3 system, which acts like a guide for the associated Cas3 helicase–nuclease enzyme, which shreds large DNA regions unidirectionally. This long-range degradation strategy is different from the precise double-strand break technology seen in the CRISPR–Cas9 system.

As TTR is mainly expressed in the liver, the study wanted to understand the efficacy of CRISPR–Cas3 in controlling hepatic TTR expression. A mouse model of ATTR and a lipid nanoparticle (LNP)-based delivery system were used for the study. Results showed that the CRISPR–Cas3 system can induce reliable, extensive deletions of the TTR gene. "Through CRISPR RNA optimization, we achieved around 59% editing at the TTR locus in our in vitro experiments. In mice model, a single LNP-based treatment helped us to achieve more than 48% hepatic editing and reduced serum TTR levels by 80%," highlights Prof. Mashimo. This system did not induce indels at the off-target sites, which is considered a major limitation for the CRISPR–Cas9 system.

The findings of this study can influence societal perspectives on genetic therapies by highlighting a safer alternative to CRISPR–Cas9, as it avoids the risk of generating unintended, potentially harmful mutant proteins. With further optimization and safety evaluation, this CRISPR–Cas3 can be established as a new and safer platform for genome-editing-based therapies, providing patients with durable, possibly one-time treatments that directly address the root genetic causes of their conditions. This can ultimately improve both life expectancy and quality of life for many individuals.

"In the coming years, this technology can lead to clinical applications not only for ATTR, but also for other currently incurable inherited diseases," explains Prof. Mashimo as the future of this technology.