Brain-directed gene editing ends in death

The child had Snijders Blok-Campeau syndrome caused by an R1025W mutation in CHD3. Researchers sought to convert the mutant adenine to guanine using a CRISPR-Cas-derived base editor, restoring the complementary cytosine without making a double-strand DNA break.

Because the editor was too large for one vector, its instructions were divided between two AAV9 vectors and injected into the spinal fluid, with both vectors required to reach the same neurons. Seven days after receiving trillions of viral particles in March 2025, the child died from thrombotic microangiopathy, which the hospital’s ethics board judged “definitely related” to the treatment.

All four monkeys in a preceding toxicology study had developed moderate-to-severe liver damage, and one high-dose animal also showed kidney injury. The hospital's ethics committee approved the single-patient trial before reviewing the final toxicology report. Experts also questioned the treatment’s likelihood of editing enough neurons, the adequacy of the primate evidence and whether its risks were properly communicated. The death was not publicly disclosed when associated preclinical research appeared in Nature on 18 February 2026.

Responding after the death was disclosed, the Chinese Society of Gene & Cell Therapy (CSGCT) said the case underscored the need for robust preclinical evidence, rigorous ethical governance, transparency and timely reporting of serious adverse events. It presented China’s new national framework for investigator-initiated research, State Council Order No. 818, as an effort to strengthen oversight and patient protection.

The investigation was led by Brendan Borrell in collaboration with Retraction Watch. It was published in Science on 23 July 2026. The additional preclinical data was published in Nature on 18 February 2026.