The earlier version gave us a window into making gene therapies safer
In a London laboratory, scientists have coaxed a dying liver back to life — at least in mice — offering the first credible hope for children born with ARC syndrome, a genetic disorder so severe that most do not survive their first year. The breakthrough, born from years of failure and refinement, centers on delivering a missing protein gene precisely to liver cells, sidestepping the cancer risk that had shadowed earlier attempts. It is a reminder that medicine's most consequential advances often arrive not in a single leap, but through the patient unlearning of what went wrong.
- ARC syndrome is a near-certain death sentence for infants — without the VPS33B protein, bile poisons the bloodstream and most children die before their first birthday.
- An earlier version of the gene therapy appeared to offer rescue, then betrayed it — roughly 30 percent of treated mice developed liver tumors, forcing researchers back to the drawing board.
- The team's critical insight was precision: by targeting the therapy exclusively to liver cells and calibrating gene expression to natural levels, they eliminated tumor development entirely.
- Treated mice survived at more than double the rate of untreated animals, and the liver scarring that defines the disease receded — proof that the approach can work.
- Human trials remain years away, but the findings reframe what is possible for ARC syndrome and a wider landscape of inherited liver diseases that currently offer families almost nothing.
At University College London and Great Ormond Street Hospital, researchers have used gene therapy to cure a disease that kills most children before their first birthday. The condition, ARC syndrome, strips the body of its ability to produce VPS33B — a protein essential for bile to flow properly from the liver. Without it, bile backs up, bilirubin and bile acids reach toxic levels, and sepsis follows. In the UK, roughly six pregnancies a year are touched by this disease. Most babies do not survive it.
The team, led by Dr. Claudiu Cozmescu, tested their approach on mice engineered to lack the VPS33B gene. When a healthy copy of the gene was delivered to these animals, the results were striking: around 80 percent of treated mice survived, compared to roughly 33 percent of untreated ones, and the liver scarring characteristic of the disease diminished significantly.
The road to that result was not clean. Earlier versions of the therapy, delivered throughout the body rather than targeted to liver cells, caused tumors in about 30 percent of treated mice — a sobering reminder that in gene therapy, the cure can become its own danger. The researchers identified the mechanism: genes were activating abnormally, triggering cancerous growth. Their response was to redesign the treatment entirely, confining it to liver cells and keeping gene expression as close as possible to natural levels. The refined approach produced no tumors while preserving the therapy's healing effect.
Professor Paul Gissen, a co-author on the study, noted that the failed early version ultimately taught the team how to make gene therapies safer — a lesson with implications well beyond ARC syndrome. Dr. Cozmescu described the findings as proof-of-concept for treating not only this disease but other inherited liver conditions that currently offer families little recourse.
Long-term toxicology and safety studies must precede any human trials, and years of work remain. But for families who have had almost nothing to hold onto, the research offers something rare and quietly profound: a reason to hope.
In a laboratory at University College London and Great Ormond Street Hospital, researchers have achieved something that seemed impossible just years ago: they have used gene therapy to cure a disease that kills most children before their first birthday. The breakthrough, published in Nature Communications, centers on a condition called ARC syndrome—a rare genetic disorder where the body cannot produce a protein called VPS33B, which is essential for bile to flow properly from the liver.
Without this protein, bile backs up in the liver and spills into the bloodstream. Bilirubin and bile acids accumulate to toxic levels, triggering sepsis. Children born with ARC syndrome have almost no chance of survival. In the United Kingdom alone, roughly six pregnancies each year are affected by this disease. Most babies do not make it past their first year.
The team, led by Dr. Claudiu Cozmescu at UCL's Great Ormond Street Institute of Child Health, tested their approach on mice engineered to lack the VPS33B gene. Some mice had no working copies of the gene in their livers; others had just one, used to test whether the treatment itself might cause harm. The disease mice developed liver problems that mirrored what happens in human children with ARC syndrome. When the researchers injected a healthy version of the gene into these animals, something remarkable occurred: the livers began functioning again. About 80 percent of treated mice survived, compared to roughly 33 percent of untreated animals. The scarring in their livers—a hallmark of the disease—diminished significantly.
But the path to this success was not straightforward. In earlier versions of the treatment, something went wrong. When the gene therapy was delivered throughout the body rather than targeted specifically to liver cells, about 30 percent of the treated mice developed liver tumors. This risk of cancer as a side effect of gene therapy has haunted the field for years, raising serious questions about whether the cure might be worse than the disease. The researchers realized the problem: the genes were becoming abnormally activated in ways that triggered cancerous growth.
They redesigned the treatment to target only liver cells, keeping the gene expression levels as close as possible to what occurs naturally in healthy tissue. The result was striking. None of the mice treated with this refined, liver-targeted version developed tumors. The therapy maintained its ability to restore liver function while eliminating the cancer risk that had plagued earlier attempts.
Professor Paul Gissen, a co-author and Clinical Professor of Paediatric Metabolic Medicine at the same institute, emphasized that the breakthrough revealed something crucial about how to make gene therapies safer. "The earlier version gave us a new window into the understanding of how to make gene therapies safer for the patients," he said. The insight—that precision in targeting and dosage matters enormously—could reshape how researchers approach other genetic diseases.
Dr. Cozmescu noted that the findings offer proof-of-concept that gene therapy could become a realistic treatment for ARC syndrome and potentially other inherited liver diseases that currently have few or no effective options. But the path from mice to human patients remains long. Before any child receives this treatment, researchers must conduct further long-term toxicology and safety studies. Years of additional work lie ahead.
The research was funded by GOSH Charity and LifeArc, a self-funded medical research organization. George Orphanides, Chief Scientific Officer at LifeArc, acknowledged that while the early findings are important, the real challenge is ensuring that promising science in the laboratory actually reaches the families who need it. For now, this breakthrough offers something that families with ARC syndrome have rarely had: genuine hope that a cure might one day exist.
Notable Quotes
Gene therapy could become a realistic treatment for ARC syndrome and potentially other inherited liver diseases that currently have few or no effective options.— Dr. Claudiu Cozmescu, UCL Great Ormond Street Institute of Child Health
The earlier version gave us a new window into understanding how to make gene therapies safer for patients. One insight is to keep gene levels as close to those found in healthy cells as possible.— Professor Paul Gissen, UCL Great Ormond Street Institute of Child Health
The Hearth Conversation Another angle on the story
Why does this particular disease matter so much for gene therapy research? There are many rare diseases.
Because ARC syndrome is so severe and so clearly genetic—one missing protein, one gene. If you can fix that one thing, you cure the disease. It's almost a perfect test case. And the stakes are absolute: these children die. There's no time for incremental improvement.
The earlier versions caused cancer in 30 percent of mice. That's a massive problem. How did they solve it?
They realized the gene was being expressed at abnormal levels throughout the body. Cancer often happens when genes are turned on too much or in the wrong places. So they redesigned the therapy to target only liver cells and to keep the gene expression as close to normal as possible. It's elegant, really—not a different drug, just a smarter delivery.
Does this mean gene therapy is finally safe?
Not universally, no. But it suggests that safety isn't impossible. It depends entirely on how the therapy is designed. You can't just inject a gene and hope. You have to think about where it goes, how much it expresses, what cells it affects. The researchers learned that the hard way.
How far away are human trials?
Years, at minimum. They need long-term safety studies first. You can't rush this with children. But the fact that they have a working, non-toxic version in mice is the crucial step. It moves from "maybe this could work" to "we have something worth testing carefully."
Six pregnancies a year in the UK. That's not many people.
It's not. But for those six families, it's everything. And the research might help thousands of children with other rare liver diseases. The science doesn't scale by prevalence—it scales by what you learn.