A Baby's DNA Was Rewritten: Nature’s Top 10 (2025) & A Historic Threshold in MedicineCategory: Science & Innovation / Medical Breakthroughs

Like many prestigious journals, Nature announces its "Top 10" list at the end of every year, revealing the boldest steps taken by science to the public. The 2025 list not only shows what science can do, but what it dared to do.

Here are three striking examples from this year's list, leading up to a historic breakthrough involving a baby who cannot yet speak.

Highlights from the List

1. Rewriting Cellular Decisions A scientist working with peptides is investigating how cells can be persuaded. There is no pressure, no force. Just very short sequences consisting of a few amino acids... But the cell recognizes them. When one peptide arrives, it stops proliferating; when another arrives, it switches to repair mode. The immune system lowers its voice; inflammation retreats. What is happening here is not just treatment; it is the rewriting of the cellular decision-making mechanism. Not large molecules, but small signals are directing the course. And this is changing the tone of biology.

2. Life in the Darkest Depths Then, our gaze shifts to where the light ends—thousands of meters below the ocean, to creatures living in depths where pressure crushes even bones. No oxygen, no sun, but there is metabolism. These microorganisms do not produce energy in the ways we know. They use chemistry differently. As they are discovered, the question changes: "Where is life possible?" This is no longer a philosophical question; it is a biochemical possibility. The darkest points of the Earth may be the first clue to other planets.

3. The Table, Not the Lab Now, we face not a glass laboratory bench, but a wooden table. States are sitting around the negotiation table. What is being discussed is not politics, but curves, transmission speeds, and mutation rates. A scientist is trying to explain that the next pandemic can be stopped not in the laboratory, but at the table. Because viruses know no borders; science shouldn't either. In this story, the hero is not a discovery, but a timely decision.

(Source: Nature’s 10. www.nature.com. 8 December 2025)

A Historic Threshold Crossed: In Vivo Base Editing

Among the stories in the 2025 list, there is an unusual "hero": a baby who cannot yet speak. And a single letter corrected in his DNA. This story showed that gene therapy performed inside a living human is no longer theory—it is a groundbreaking reality.

The Silent Struggle The story begins with a disease: Carbamoyl-phosphate synthetase 1 (CPS1) deficiency. A rare, but ruthless metabolic disorder. KJ Muldoon began showing critical symptoms immediately after birth in August 2024; high levels of ammonia were detected in his blood. Due to a change in the gene, the body's capacity to render ammonia harmless collapses. Ammonia levels rise, the brain is severely affected, and for most babies, the first months are a struggle for survival. The statistics are cold: approximately 50% mortality in early infancy. But there is something statistics do not write about: the silence in families' waiting rooms.

The Microscopic Error For Baby KJ, the problem was actually microscopic. A single base letter in the CPS1 gene was incorrect. Just one among billions of letters in the DNA. A letter that should have been C or G was, at just one point, T. But biology sometimes puts a single letter in front of a whole life. For many years, medicine's answer was clear: managing the result (diet, drugs, transplant) rather than fixing the cause.

The "Pencil" Instead of Scissors What makes 2025 a "Nature Top 10" moment starts here. Scientists led by Prof. Kiran Musunuru targeted the cause, performing this treatment not in theory, but in a baby's liver.

You have likely heard of CRISPR technology. But the method used here is a more elegant technique called Base Editing. Unlike the classic CRISPR-Cas9 "scissors" that cut DNA, Base Editing works like a pencil. It changes the incorrect letter to the correct one without cutting or breaking the DNA.

• Standard CRISPR: Cuts the DNA, risking unwanted changes.

• Base Editing: A "non-cutting" Cas9 acts as a guide, carrying an enzyme that simply changes a single letter (e.g., C → T or A → G).

It works quietly, is less stressful for the cell, and is particularly effective in rare genetic diseases caused by single-letter errors.

A First in History This was exactly what was done for KJ. Base editing fixed the error on site. No genes were added, no DNA was cut. The cell returned to its own job.

This treatment was designed from scratch for KJ. RNA guides specific to his mutation were written, and regulatory enzymes were selected, all placed inside lipid nanoparticles to find their way to the liver. It was a race against time, with diagnosis to treatment measured in weeks. But what happened inside the cell was a step medicine has dreamed of for centuries: the genetic correction of a disease-causing letter inside a living human's DNA.

The Outcome & The Future After just two applications, the baby's lethally high ammonia levels were brought under control. Protein levels in the diet could be increased, and drug doses reduced. KJ survived.

This is the moment the concept of "Personalized Medicine" stepped out of the laboratory and into real life. Genetic cardiologist Kiran Musunuru had been striving for this moment for many years. The same genome can be rewritten according to different mutations—today CPS1, tomorrow cardiovascular diseases via ANGPTL gene editing.

In 2025, science did not just produce new information; it opened a new moral, legal, and philosophical field. While other Top 10 stories looked at the universe or oceans, this story looked inside the human being and said, "We can fix it if we want to." That is why KJ's story is not a case report. It is a threshold. A paradigm shift.

Further Reading Suggestions:

1. Musunuru K, Grandinette SA, Wang X, et al. Patient-Specific In Vivo Gene Editing to Treat a Rare Genetic Disease. N Engl J Med. 2025;392(22):2235-2243.

2. Nature’s 10: www.nature.com/immersive/d41586-025-03848-1/index.html

3. CHOP–Penn Medicine Gene Therapy Consortium. First-in-human personalized CRISPR base-editing therapy for CPS1 deficiency. Nat Med. 2025;31:1021-1028.