New Treatments7 August 2026

Bespoke medicines: genetic therapies designed for a single child

Doctors have begun designing genetic medicines for one patient at a time. The science is moving faster than the regulatory and funding models built around it.

By NextGenHealth Editorial Team2 min read

A textured DNA double helix against a soft blue background — Photo: digitale.de / Unsplash

In brief

From milasen to bespoke base editing, genetic medicines are being designed for single children. The science, the regulatory hurdles and who pays.

In 2018, a team in Boston designed an antisense oligonucleotide for a single girl with a fatal neurodegenerative disease caused by a mutation found in almost no one else. The drug, named milasen after her, went from genetic diagnosis to first dose in about a year. The case, published in the New England Journal of Medicine in 2019, showed that a genetic medicine could be built for one person.

From one-off to a model

Antisense oligonucleotides are well suited to this. Their chemistry is modular: the backbone stays the same, and only the sequence changes to match the target. Once a platform’s safety is understood, a new sequence for a new mutation can, in principle, be designed and made quickly.

Gene editing has followed. In 2025, clinicians in Philadelphia reported treating an infant with a severe inherited metabolic disorder using a base-editing therapy designed specifically for his mutation, delivered within months of birth.

The bottlenecks

The barriers are not mainly scientific.

Regulation. Drug regulation was designed for products tested in large numbers of patients. Individualised therapies are usually given under expanded access or single-patient research approvals, which each take time and expertise to secure.
Manufacturing. Every bespoke drug still needs to be made to clinical standards and tested for safety.
Funding. There is no commercial market for a medicine that one person will take. Most cases so far have relied on philanthropy, academic budgets and non-profit organisations set up for this purpose.

What comes next

Regulators have begun discussing frameworks that would let a platform’s safety data carry across multiple individualised products, so that each new sequence does not start from zero. If that happens, children with ultra-rare mutations could one day have a realistic route to treatment rather than an extraordinary exception.

N-of-1 therapies
Antisense oligonucleotides
Base editing
Rare diseases

More in New Treatments. Pipelines, approvals and first-in-child therapies, from small molecules to gene editing.

Treatments

Three ways to treat spinal muscular atrophy

In less than four years, a disease with no treatment gained three, each using a different technology. SMA has become a case study in how modality shapes access.
Treatments

Gene therapy’s pipeline is overwhelmingly paediatric

Many of the conditions that one-time genetic treatments target first appear in infancy. That puts children at the centre of the field’s scientific, commercial and ethical debates.
Treatments

CAR-T began with children: the paediatric origins of cell therapy

The first CAR-T therapy approved anywhere was for children and young adults with leukaemia. That history still shapes how the field thinks about paediatric patients.
Treatments

CFTR modulators and the push to treat cystic fibrosis earlier

Drugs that correct the underlying protein defect have changed cystic fibrosis. The next question is how early in life they should start.
Treatments

Gene editing reaches the clinic: what CRISPR therapy means for younger patients

The first approved CRISPR-based medicine treats sickle cell disease from age 12. Extending it to younger children raises questions about conditioning, fertility and timing.
All New Treatments 6 articles

Conditions

Rare diseases set the agenda for paediatric drug development

Many rare conditions begin in childhood, so orphan drug incentives and paediatric rules increasingly pull in the same direction.
Policy

The rare pediatric disease priority review voucher, explained

A tradable right to faster FDA review has become one of the more valuable prizes in paediatric drug development. Whether it creates new medicines is still debated.
Evidence

Neonates: the least studied patients in medicine

The babies in neonatal intensive care receive some of the most intensive drug treatment in medicine. Very little of it was ever tested in them.
Policy

Why children still wait years for medicines adults already have

Two decades of incentives and mandates on both sides of the Atlantic have transformed paediatric drug development. They have not closed the gap.
Medicines

The formulation problem: making adult drugs work for small bodies

A tablet that suits a 70kg adult is often useless for a toddler. Getting the dose, the taste and the ingredients right is a development programme in its own right.
Evidence

Extrapolation is changing how paediatric trials are designed

Regulators increasingly accept that adult efficacy data can carry over to children when the disease and the drug’s effect are similar enough. The argument is about how much.