When Emmanuelle Charpentier and Jennifer Doudna were awarded the 2020 Nobel Prize in Chemistry, few outside the scientific community realized the full significance of their discovery. Six years later, CRISPR gene editing is transforming medicine.
For thousands of patients, it is offering hope where conventional medicine has failed or could do nothing because the fault lies in the genetic makeup of the patient. Scientists are now exploring whether the technology could one day correct the genetic changes responsible for conditions such as Down syndrome, potentially reducing the number of abortions following prenatal diagnosis each year.
The field has already reached remarkable clinical milestones. In 2025, baby KJ Muldoon became the first person in the world to receive a bespoke CRISPR gene-editing treatment designed specifically for his DNA. Born with an ultra-rare genetic disorder known as severe carbamoyl phosphate synthetase 1 (CPS1) deficiency, he was unable to process ammonia, allowing toxic levels to build up in his blood and putting him at constant risk of irreversible brain damage or death.
Doctors and researchers developed a personalized treatment in just a few months, delivering the gene-editing therapy directly to his liver. Within weeks, KJ's condition had stabilized. He was able to tolerate more protein in his diet, required fewer ammonia-lowering medications and avoided a liver transplant, previously his only realistic chance of survival. His case marked the first successful use of a tailor-made CRISPR therapy in a single patient and is widely regarded as a landmark in the era of personalized genetic medicine.
Sadly, not every patient has benefited from gene editing. Among them was six-year-old Mei, not her real name, from China, who died after undergoing experimental CRISPR gene-editing treatment at Xinhua Hospital. The hospital, which is affiliated with the Shanghai Jiao Tong University School of Medicine, is acclaimed for its pediatrics department.
Desperation Leading Parents to Seek Experimental Treatment
Mei's parents first became concerned when she started falling behind other children in her development. At six years old, she still spoke only in simple sentences and ate with training chopsticks. Genetic testing eventually identified the cause: a single mutation in her DNA. A C had been replaced by a T.
Hoping to find a treatment, her parents turned to acclaimed Chinese neuroscientist Zilong Qiu at Shanghai Jiao Tong University. He was among a handful of researchers around the world working to develop personalized treatments using base editing, a more precise version of the gene editing technology CRISPR, for children with rare genetic diseases.
Understandably, Qiu had hoped to be hailed as a hero, like the scientists who treated baby KJ Muldoon. But in this case the gene editing was not performed on a terminally ill child. Mei's condition was not considered immediately life threatening, and doctors regarded her as having a relatively mild form of the genetic disorder. Her parents feared that, without treatment, she would never be able to live independently or care for herself. As the parents of an only child, they also faced intense pressure in a society where expectations of children's academic achievement and future success are exceptionally high.
Mei's parents raised $860,000 to fund Qiu's research, first in mice and later in monkeys, before the treatment could be tested in their daughter.
One of the biggest challenges with CRISPR is delivering the gene editing machinery to the right cells. To alter a person's DNA, scientists typically use specially engineered viruses to carry the editing system into cells, where it can make the desired changes. Qiu also proposed delivering the virus into the spinal fluid rather than the blood to bypass the internal organs and prevent damage.
Once the viral vector had been developed by Qiu's colleague and Rett syndrome patent co-inventor, Kan Yang, the team was ready to proceed. According to Mei's parents, however, Qiu did not disclose the adverse reactions observed in the primates during the preclinical studies. The researchers later published their findings in Nature, but peer reviewers raised concerns about the quality of the proof-of-concept study in monkeys. Among the issues highlighted was the absence of control samples to demonstrate that the staining selectively identified the gene editor.
Mei was admitted to hospital with her parents and received the viral vector through an injection into her spinal fluid. Before the procedure, doctors warned the family that the greatest risk was an immune reaction to the viral vector. To reduce that risk, Mei was given a steroid beforehand. Today, many researchers favor stronger immunosuppressive drugs, such as rapamycin and rituximab, as a precaution.
Mei developed a fever, a common side effect, but she also suffered acute kidney injury and later died. According to her parents, they had not been warned that the treatment carried a risk of death during what was effectively a first-in-human clinical trial.
That decision, along with other aspects of the treatment, might have received greater scrutiny had the trial been reviewed as a commercially sponsored study by China's National Medical Products Administration, the country's equivalent of the US Food and Drug Administration, rather than as an investigator-initiated trial. Critics argue that the less stringent review process allowed the experimental treatment to proceed with fewer safeguards than would normally be expected for a commercially sponsored clinical trial.
Who Is at Fault for Mei's Death and Should This End CRISPR?
Ultimately, Qiu proceeded with the treatment despite knowing the adverse reactions that had occurred in his animal experiments and, according to Mei's parents, without fully disclosing those risks. He appeared intent on achieving a scientific breakthrough and publishing his work in Nature. If that account is accurate, it represents a serious breach of medical ethics. The principle of “first, do no harm” requires physicians to ensure that patients, or in this case their parents, fully understand the risks before consenting to an experimental procedure.
Mei's parents also made a difficult decision. Their daughter was not terminally ill, but they feared she would never be able to live independently. They had struggled for four years to conceive their only child, and it is difficult to ignore the wider social context. Decades of China's one-child policy, combined with intense social and economic pressure on families, have created powerful incentives for parents to seek every possible advantage for their children.
The case also recalls another major ethical scandal in Chinese genetics. In 2018, scientist He Jiankui shocked the world by editing the genomes of human embryos that later resulted in the birth of three children, crossing a line that much of the international scientific community considered unacceptable.
Gene editing holds enormous promise for treating severe and life-threatening diseases. Increasingly, however, researchers are exploring applications that go beyond preventing death or serious illness and extend to modifying characteristics that may one day include intelligence, height or other complex traits. Such possibilities demand far greater ethical scrutiny.
China's determination to accelerate technological innovation appears to have been accompanied, in some cases, by a deliberately less stringent regulatory framework than that found in the United States and Europe. When experimental gene editing is performed on patients who are not terminally ill, the threshold for safety, oversight and informed consent should be exceptionally high. In such cases, the potential benefits must clearly outweigh the risks.
