Gene editing works by tweaking the molecular building blocks of DNA, known as bases, to restore the normal function of a mutated gene.
CRISPR is the dominant gene-editing tool, invented in 2012 by Jennifer Doudna and Emmanuelle Charpentier, who won the Nobel prize in chemistry in 2020 for the work. A CRISPR drug uses an enzyme known as an editor, guided to the right place in the genome by an RNA molecule designed to match the target stretch of DNA. Conventional CRISPR edits genes by excising or inserting bases. To work, CRISPR first breaks the DNA double helix for the cell to subsequently fix it; how well the repairs work in human embryos is unclear, as breaks might be left unmended or the ends of the DNA helix may pair up in unusual ways, causing new mutations.
Casgevy, the first licensed gene-editing treatment, cures people of sickle-cell disease. It is made by Vertex Pharmaceuticals and CRISPR Therapeutics and currently costs around $2m per dose. The treatment requires a patient's bone-marrow stem cells to be collected, sent to a lab for editing, and then transplanted back.
Base editing is a newer variant of CRISPR that chemically converts one base into another rather than cutting and inserting. In all other respects it works like conventional CRISPR.
Base editing was invented at the Broad Institute in Cambridge, Massachusetts, in 2016. Verve Therapeutics, a Boston-based biotech firm, is using base editing to develop a drug that could treat heart disease by turning off a cholesterol-raising gene in the liver, at an expected cost of $2bn.
In 2024-25 a team at the Children's Hospital of Philadelphia and the University of Pennsylvania created the first gene-editing drug designed for a single patient. The patient, a baby known as KJ, was born in Philadelphia in August 2024 with carbamoyl-phosphate synthetase 1 (CPS1) deficiency, a rare genetic disease that often kills in infancy and for which no good neonatal treatment exists. CPS1 normally helps turn ammonia—produced when the gut digests protein—into another chemical excreted with urine. Without the working enzyme, ammonia build-up poisons the brain, leading to coma and death.
Rebecca Ahrens-Nicklas, a metabolic-disease expert, and Kiran Musunuru, a geneticist, developed a base-editing drug targeting KJ's unique mutation in under two months, working in human cells modified to carry his mutation. In mice engineered with the same mutation, about 42% of liver cells were edited. Following safety tests in monkeys, America's Food and Drug Administration gave permission to treat KJ.
KJ received three intravenous doses between February and April 2025. The editors were delivered using lipid nanoparticles—the same fat-bubble vehicle used for covid-19 mRNA vaccines—which carry the drug naturally to the liver. His ammonia levels improved significantly and remained normal even when he contracted a virus, a situation that would typically send ammonia levels soaring in CPS1-deficient children. KJ became the first person treated with a bespoke gene-editing therapy.
Fyodor Urnov of the Innovative Genomics Institute at the University of California, Berkeley, connected the team with Danaher, a life-sciences company that produced the editor. Dr Urnov hopes that diagnosis, production, testing and approval of bespoke gene-editing therapies could one day be done in less than a month.
In 2018 He Jiankui, a rogue Chinese scientist, created the world's first gene-edited babies in secret using CRISPR—a reckless and illegal act. Since then new efforts to create gene-edited babies have emerged, this time promoted and funded by Silicon Valley billionaires. Preventive, an American startup founded by Lucas Harrington (a former student of Jennifer Doudna's), raised $30m from investors including Brian Armstrong, head of Coinbase, and Oliver Mulherin, husband of Sam Altman. The company says it will focus on research to establish whether embryo editing is safe, ultimately with the goal of preventing severe genetic diseases. Manhattan Genomics, co-led by Cathy Tie, a serial biotech entrepreneur, is another firm in the area.
In principle, editing a single-celled embryo could overcome the delivery problems and cost of therapies like Casgevy; Dr Harrington estimates the cost could fall to $5,000 per embryo. But edits made in embryos would be passed on to future generations, with unpredictable consequences. It is currently illegal for the Food and Drug Administration to consider applications for trials of embryo editing.
ASOs are short synthetic molecules that work by ambushing RNA messenger molecules carrying genetic instructions from a cell's nucleus to its protein factories, then either neutralising or altering them. Unlike CRISPR, ASOs do not edit DNA directly; they must be given over a lifetime rather than as a single dose. The first ASO designed for a single patient was developed for Mila Makovec at Boston Children's Hospital; she died in 2021 aged ten.
Around 300m people worldwide are affected by rare diseases, 80% of which are caused by faulty genes. Breakthroughs in genomics and genomic medicines mean more are treatable, yet sufferers are seldom treated. Drug firms have little incentive to develop custom medicines; the process is costly for businesses set up to make drugs at scale. Probably fewer than 100 customised drugs for rare diseases have been made since 2018, usually paid for by desperate parents through charity.
In January 2026 Britain's Medicines and Healthcare products Regulatory Agency (MHRA) approved a novel clinical trial under a "master protocol" that standardises trials for the treatment of groups of genetic conditions within a single framework—testing a way of making drugs rather than assessing a single medicine. Ten children, each suffering from an ultra-rare genetic neurodegenerative disease, will each receive a unique ASO. If the trial succeeds, the MHRA will approve the process of making custom drugs rather than each custom drug individually—a regulatory first. The firm doing the tailoring, EveryONE Medicines, would then be able to make as many variants as there are treatable children in Britain.
The first patient was treated on January 13th 2026 at Great Ormond Street Hospital. In 2023 the MHRA, Genomics England (a government-owned provider of genetic-sequencing data) and Mila's Miracle Foundation teamed up with experts at Oxford University to create the Rare Therapies Launch Pad to work out how to regulate custom drugs. In November 2025 America's Food and Drug Administration said it was developing a similar "plausible mechanism" pathway. In Europe, an academic group called 1 Mutation 1 Medicine is trying to advance ASO-based treatments.
The MHRA's innovation takes seriously the trade-off between the unknown risk of customised treatment and the almost inevitable suffering in its absence. EveryONE Medicines reckons process approval could cut the cost of developing custom therapies from $2m-3m to below $1m and the time from two to three years to less than nine months.
Process approval should also allow firms that use other ways of interfering with RNA messengers, and those that edit DNA directly, to consider treating ultra-rare disorders. Aurora Therapeutics, a gene-editing firm, was launched on January 9th 2026 by Jennifer Doudna.
CRISPR is increasingly used to alter fruit and crop plants. Unlike earlier genetically modified crops, CRISPR-edited plants do not require DNA from a foreign organism to be inserted—a practice that puts consumers off. The technology permits the deletion of single genes, enabling changes hard to achieve through conventional breeding.
Pairwise, a biotech company in North Carolina, is developing seedless blackberries and stoneless cherries. GreenVenus, a Californian firm, is using CRISPR to develop non-browning avocados by obstructing polyphenol oxidase, an enzyme responsible for oxidation. Scientists have also developed mushrooms and potatoes that oxidise more slowly. In 2021 a Japanese tomato with higher GABA content became the first CRISPR food to go on sale. In 2024 scientists in China used CRISPR to make tomatoes up to 30% sweeter by disabling genes that limit sugar production.
Progress is slower with tree fruits because it takes several years for apple or peach trees to begin bearing fruit from an altered seed. AI and computational modelling are helping scientists discover more quickly how multiple genes and biochemical pathways produce complex traits such as flavour.
In 2016 Argentina became the first country to rule that gene-edited products should be regulated in the same manner as conventionally bred ones. In December 2025 the European Union's Parliament and Council reached a provisional deal to simplify the process for marketing plants bred through new genomic techniques, including scrapping the requirement to label them differently from conventional products.
Epigenetic editing is a related but distinct approach that uses the same CRISPR guidance system but disables the cutting enzyme, instead attaching chemical markers to the genome or its histone scaffolding to modulate gene activity without altering DNA. Several firms founded by CRISPR pioneers, including Scribe Therapeutics (co-founded by Jennifer Doudna) and Epic Bio (founded by Stanley Qi), are pursuing clinical applications.
AI is being used to design new CRISPR-Cas gene-editing tools. The Institute for Protein Design at the University of Washington is working on custom-targeted nucleases—the "Cas" part of CRISPR-Cas complexes—designed to bind to particular DNA sequences, increasing the range of DNA that can be edited and reducing the risk of off-target edits. Profluent, a firm in Emeryville, California run by Ali Madani, is focused on creating new CRISPR-Cas tools using AI models trained on a curated database of around 5m CRISPR-Cas protein complexes.
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