A team of scientists in Japan has reported progress in using the CRISPR–Cas3 gene-editing system to treat transthyretin amyloidosis (ATTR), a genetic disorder characterized by the accumulation of misfolded transthyretin proteins, which mainly affects the heart and nerves. ATTR can lead to heart failure and neuropathy, with one form caused by inherited mutations in the TTR gene.
Existing treatments, such as RNA interference-based drugs, can reduce TTR protein production but require ongoing administration and do not cure the disease. Gene-editing technologies offer potential for permanent correction of genetic disorders. While CRISPR–Cas9 is widely known for its ability to edit DNA, it has limitations including unintended cuts that may cause harmful effects.
Researchers led by Professor Tomoji Mashimo and Dr. Saeko Ishida at the Institute of Medical Science, The University of Tokyo, have evaluated CRISPR–Cas3 as an alternative tool. "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," said Prof. Mashimo regarding his motivation for the study.
CRISPR–Cas3 differs from CRISPR–Cas9 in both structure and function. Whereas Cas9 uses a guide RNA and acts like molecular scissors to make precise cuts in DNA, Cas3 operates through a multiprotein complex that guides an enzyme capable of shredding large regions of DNA unidirectionally—a different approach from Cas9's double-strand breaks.
To test efficacy, researchers used a mouse model of ATTR along with a lipid nanoparticle-based delivery system targeting liver cells where TTR is primarily produced. "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%," Prof. Mashimo noted. Importantly, this approach did not produce unintended edits at other locations—a common issue with Cas9 systems.
The study suggests that CRISPR–Cas3 could offer safer alternatives for gene therapy compared to existing methods by reducing risks associated with off-target effects and mutant protein formation. With further development and safety checks, this technology could enable long-lasting treatments that address underlying genetic causes rather than just managing symptoms.
"In the coming years, this technology can lead to clinical applications not only for ATTR, but also for other currently incurable inherited diseases," said Prof. Mashimo about future prospects for CRISPR–Cas3 therapies.
