World’s First Baby Treated with Personalized CRISPR Gene Editing

1. In May 2025, a 9-and-a-half-month-old baby boy named KJ Muldoon became the 1st patient in the world to receive a personalized gene-editing treatment using the CRISPR technology.
2. This historic treatment took place in Philadelphia and it also represents a huge step forward in medicine, especially for people with rare genetic diseases.

What Condition Did KJ Have and what is CPS1 deficiency ?

1. KJ was born with a very rare and serious genetic disease called CPS1 deficiency (short for carbamoyl phosphate synthetase 1 deficiency).
2. This disease is caused by mutation in one of KJ’s genes.
3. Genes are like instruction manuals inside our cells that tell the body how to work properly.
4. The gene mutation in KJ caused a problem that stopped his body from making an important enzyme needed for his liver to work properly.
5. Without this enzyme, harmful waste called ammonia builds up in his body, which can be very dangerous and sometimes fatal.
6. Usually, children with this condition need a liver transplant to survive.

What is a Mutation?   A mutation is a change or mistake in the DNA sequence — the instructions inside our cells that tell the body how to grow, develop, and function. DNA is made up of millions (actually billions) of tiny chemical building blocks called bases, often represented by the letters A, T, C, and G. These letters form a code, kind of like the letters in a sentence or words in a book. A mutation happens when one or more of these letters is changed, added, or missing. This can change the message that the DNA is sending. Why Do Mutations Matter? Our DNA instructions tell our cells how to make proteins, which do most of the work in our bodies — like building tissues, helping organs function, fighting infections, and more. If the DNA code is changed by a mutation, the protein made might: Work incorrectly or not at all. Be made in the wrong amount. Sometimes, the change might have no effect at all. When a mutation affects an important gene — especially one that makes a crucial protein — it can cause genetic diseases or increase the risk of health problems. How Do Mutations Happen? Mutations can happen in many ways: Naturally, when DNA is copied during cell division, small mistakes sometimes occur. Due to environmental factors like radiation, chemicals, or viruses. Mutations can be inherited from a parent if they are present in sperm or egg cells.

Why Was This So Serious?

1. For babies born with CPS1 deficiency, Without treatment, many children either die young or require a liver transplant — a risky procedure with a lifetime of follow-up care and potential complications.
2. The usual treatments were harsh and limited: KJ had to eat a very restricted diet low in protein and take special medicines to reduce ammonia.

What is CRISPR-Cas9?

1. CRISPR-Cas9 is a powerful gene-editing tool that works like tiny scissors and it is also able to cut and fix DNA — the chemical instructions inside our genes.

2. It helps researchers to remove, add, or alter parts of the DNA in a very precise and controlled way.

3. It can be programmed to find and repair very specific mistakes or mutations in the genome.

4. This technology won the Nobel Prize in Chemistry in 2020 because of its potential to cure diseases caused by genetic mutations.

How Does CRISPR-Cas9 Work?

The CRISPR-Cas9 system is made up of two main parts that work together like a pair of tiny, smart scissors:

1. Cas9 Enzyme: This is a special protein that acts like molecular scissors. It can cut through both strands of DNA at a very specific spot.

2. Guide RNA (gRNA) :  This is a small piece of RNA (a close cousin of DNA) that has been carefully designed by scientists to find and stick to a specific sequence in the DNA.

3. It’s about 20 letters long and helps Cas9 know exactly where to cut.

The Process Step-by-Step

1. The guide RNA searches through the DNA inside a cell, looking for the exact matching DNA sequence it was designed to find.

2. When it finds this matching spot, it binds tightly to the DNA there, like a GPS directing the scissors.

3. The Cas9 enzyme follows the guide RNA and cuts both strands of the DNA at that exact spot.

4. The cell sees this cut as damage and activates its natural DNA repair system.

5. Scientists can then use the cell’s own repair machinery to make changes to the DNA, such as fixing a mutation, removing a faulty piece, or inserting a new piece of DNA.

But How Did It Help in the case of this baby ?

1. What made KJ’s treatment unique was that it was personalized, meaning the therapy was specially designed for the exact mutation in his gene.

2. Scientists studied KJ’s DNA and created a customized version of CRISPR that could find and fix his specific gene error.

3. This personalized medicine was delivered as an infusion (a special liquid medicine) into KJ’s body.

4. They delivered this medicine using tiny fat particles called lipid nanoparticles, which protect the gene-editing tools as they travel to the liver.

5. The treatment traveled through his bloodstream to his liver cells.

6. Once inside, the molecular scissors cut the faulty DNA sequence and corrected it, allowing the liver to start making the right enzyme again.

Why Is This Treatment a Big Deal?

1. This treatment marks the first time personalized CRISPR gene editing has been used successfully in a human patient.

2. Most previous gene-editing therapies have targeted more common diseases where many patients share the same gene mutations — like sickle cell disease or beta thalassemia.

3. But many genetic diseases are rare, each caused by unique mutations that affect only a handful of people worldwide.

4. Until now, it wasn’t clear if gene editing could be customized for individual patients quickly and safely.

5. KJ’s case shows it is possible to design a unique therapy for one patient’s specific genetic problem — and that it can work well in real life.

This is why CRISPR-Cas9 is revolutionizing biology and medicine, making it possible to treat genetic diseases, improve crops, and study how genes work in amazing new ways.

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