In 2018 a Chinese scientist announced that he had edited the genes of two embryos and that the twin girls born from them were healthy. The reaction was close to universal condemnation. He was sentenced to three years in prison the following year. The episode didn't stop gene editing. It did force a harder question into view: who decides which genetic conditions are worth editing away?
What CRISPR actually does
CRISPR-Cas9 is a pair of molecular tools borrowed from bacteria, which use it to chop up invading viruses. In 2012 Jennifer Doudna and Emmanuelle Charpentier showed it could be programmed to cut DNA at a chosen spot. Researchers can then disable a gene or, with more effort, rewrite a few letters of it. The pair won the Nobel Prize in Chemistry in 2020.
It's cheaper and faster than earlier methods, which is why labs around the world adopted it within a few years. It isn't perfect. The cuts can land in the wrong place, and changes can have effects nobody predicted.
The line between treating and enhancing
Two distinctions do most of the work in this debate. The first is between somatic and germline editing. Somatic editing changes cells in one person, such as blood cells, and the change dies with them. Germline editing changes eggs, sperm or embryos, so the edit is inherited by every later generation. Most countries allow research on somatic therapies and restrict or ban germline editing for reproduction.
The second distinction is between treatment and enhancement. Fixing the mutation behind sickle cell disease looks like medicine. Raising a child's expected height or memory looks like something else. The trouble is that the boundary isn't sharp. Is lowering the risk of heart disease treatment or enhancement? What about a mutation that makes a person resistant to HIV?
The first real therapy
In late 2023 the UK and then the US approved Casgevy, the first CRISPR-based treatment, for sickle cell disease and a related blood disorder called beta thalassaemia. It edits a patient's own blood stem cells outside the body and returns them, which switches on a form of haemoglobin that works properly. Early results were striking for patients who had spent years in and out of hospital.
It also arrived with a list price of around two million dollars in the US. Sickle cell disease is most common among people of African, Indian and Middle Eastern descent, and most of those patients live where a therapy that expensive isn't remotely available. A cure that reaches only the wealthy is a different kind of ethical problem from the one about embryos.
Who gets to define a disease
Disability scholars have long pointed out that what counts as a condition to be fixed is partly a social judgment. Some deaf people see deafness as a culture and a language, not a defect. Parents with achondroplasia have said they wouldn't choose to eliminate the trait in their children. Others living with severe, painful illnesses see the question very differently, and their view carries weight too.
If editing becomes safe and cheap, the risk is that market preferences and fashion, not need, set the list. History offers a warning. Early twentieth-century eugenics programmes also began with talk of preventing suffering.
Where this leaves us
There's broad agreement on a few points. Safety has to be shown first, consent matters, and germline editing for reproduction isn't ready. Beyond that the argument is about how much weight to give individual choice, and who gets a seat at the table when the rules are written. Patients, disability communities and people from countries that can't afford the technology belong there along with scientists. The science is moving faster than the conversation about it.
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