Doctors Built a Custom Gene Therapy for One Baby. It Worked.

A therapy designed from scratch, for one patient, stopped a fatal disease.

She was five when treatment began. Her cells couldn't make a protein that repairs DNA. Without it, kids like her don't make it past childhood. Doctors told her parents there was no cure.

Then they built one anyway.

Six Months to Design a Treatment

The child had a rare genetic disorder called Cockayne syndrome. Her body couldn't produce a protein called CSB, which fixes DNA damage. Cells accumulated errors. Organs failed. Most kids with this condition die before age five.

Researchers at Great Ormond Street Hospital and University College London designed a CRISPR-based gene therapy specifically for her genetic mutation. Not a treatment for Cockayne syndrome generally — a treatment for her mutation.

They had six months.

How It Worked

Standard gene therapy tries to insert a working copy of a broken gene. That works for some diseases, but not this one. The CSB gene is too large to fit into the viral delivery vehicles that carry genetic cargo into cells.

So they tried something different. They used CRISPR to edit the broken gene directly, fixing the mutation that stopped it from working.

They tested it in cells grown from her skin. The edited cells started producing the missing protein. Then they tested safety in animals. Everything checked out.

Last year, she received the treatment. Her body started making CSB protein. DNA repair kicked in. The disease progression stopped.

She's alive. The therapy worked.

The Future Just Arrived

This isn't the first time CRISPR has treated disease. It's the first time anyone designed a completely custom gene therapy for a single patient and deployed it successfully.

The price tag was enormous. The time investment was massive. But it proved something: we can now build therapies for individual patients with ultra-rare mutations, not just diseases with thousands of cases.

Three years ago, this would've been science fiction. Now it's peer-reviewed medicine.

What It Means

There are roughly 7,000 known rare genetic diseases. Most affect fewer than 200,000 people. Many affect fewer than 100. Drug companies don't develop treatments for markets that small — there's no business case.

But if you can design a therapy in six months, test it quickly, and deploy it for one person, the economics change. Not overnight. Not for everyone. But the door just opened.

The girl who received this treatment is doing well. Her family calls it a miracle. Her doctors call it proof of concept.

Both are right.

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Source: Great Ormond Street Hospital / University College London research published February 2026