Mie University removes extra chromosome 21

Mie University researchers reported in February 2025 that they used CRISPR-Cas9 to remove an extra copy of chromosome 21 from human cells derived from people with Down syndrome, according to the university and the paper published in PNAS Nexus. The work was done in vitro, not in patients, and the university described it as proof-of-concept at the cell level. (mie-u.ac.jp) The paper was published online on February 18, 2025, and the university issued its release on February 19, 2025. ### What exactly did the Mie University team say it removed? Ryotaro Hashizume of Mie University’s Graduate School of Medicine led the study, which targeted the third copy of chromosome 21 found in trisomy 21 cells, the university said. (academic.oup.com) Down syndrome is caused by trisomy 21, meaning cells carry three copies of chromosome 21 instead of the usual two. The PNAS Nexus abstract said the researchers used “allele-specific multiple chromosome cleavage” with CRISPR-Cas9 to eliminate the target chromosome from trisomy 21 induced pluripotent stem cells and fibroblasts. That means the reported result was chromosome removal in cultured human cells, not editing in an embryo, fetus or living person. (mie-u.ac.jp) ### How effective was the chromosome removal in the reported experiments? Mie University said the team removed the extra chromosome 21 with a success rate of up to 37.5%. The university’s Japanese and English releases both used that figure. The paper abstract, as surfaced by Oxford Academic, said the approach achieved trisomy rescue in induced pluripotent stem cells and fibroblasts. (mie-u.ac.jp) The university said the method also worked in differentiated cells and non-dividing cells, expanding the reported cell types beyond dividing stem-cell cultures alone. (academic.oup.com) ### What changed in the cells after the extra chromosome was removed? Mie University said cells whose chromosome number was normalized showed restored gene expression patterns, cell proliferation speed and antioxidant capacity. The Japanese release also said gene expression patterns and other cellular characteristics returned to normal in corrected cells. (mie-u.ac.jp) Those are the findings behind social-media descriptions that the work “normalized gene expression” and reduced cellular stress-related features. The university’s wording referred specifically to restored antioxidant capacity and cell-growth characteristics in corrected cells. (mie-u.ac.jp) ### Was this a treatment for people with Down syndrome? The February 19, 2025 university release said the result was “proof-of-concept” for eliminating the extra chromosome at the cell level outside the body. The release did not describe a clinical trial, patient dosing or use in living people. MedicalXpress, citing the paper, said the researchers suggested similar approaches could eventually be used in neurons and glial cells. (mie-u.ac.jp) That statement was framed as a future possibility, not a current medical application. ### Who conducted the study and where was it published? The paper listed Ryotaro Hashizume, Sachiko Wakita, Hirofumi Sawada, Shin-ichiro Takebayashi, Yasuji Kitabatake, Yoshitaka Miyagawa, Yoshifumi S. (mie-u.ac.jp) Hirokawa, Hiroshi Imai and Hiroki Kurahashi as authors. It appeared in PNAS Nexus, volume 4, issue 2, with DOI 10.1093/pnasnexus/pgaf022. Mie University said Hashizume is a lecturer in its Graduate School of Medicine and identified pathology, genetics and regenerative medicine among his research areas. (mie-u.ac.jp) The university also named Takebayashi, a professor in the Graduate School of Bioresources, as part of the joint research group in its Japanese release. (medicalxpress.com) ### Why did the story resurface in May 2026? An X post dated May 16, 2026 circulated the study again and linked to Mie University material and the paper, but the underlying research itself was published in February 2025. The university’s own pages and the PNAS Nexus record both place the publication in mid-February 2025. (academic.oup.com) As of May 18, 2026, the publicly verifiable record tied to this claim remains the February 18, 2025 PNAS Nexus article and Mie University’s February 19, 2025 release. Those sources are the next place to look for any follow-up from Hashizume’s group or additional peer-reviewed work. (academic.oup.com) (mie-u.ac.jp)