By  LAURA UNGAR

Associated Press

A baby born with a rare and dangerous genetic disease is growing and thriving after getting an experimental gene editing treatment made just for him.

Researchers described the case in a new study, saying he’s among the first to be successfully treated with a custom therapy that seeks to fix a tiny but critical error in his genetic code that kills half of affected infants. Though it may be a while before similar personalized treatments are available for others, doctors hope the technology can someday help the millions left behind even as genetic medicine has advanced because their conditions are so rare.

“This is the first step towards the use of gene editing therapies to treat a wide variety of rare genetic disorders for which there are currently no definitive medical treatments,” said Dr. Kiran Musunuru, a University of Pennsylvania gene editing expert who co-authored the study published Thursday in the New England Journal of Medicine.

Knowing KJ’s odds, parents Kyle and Nicole Muldoon, both 34, worried they could lose him.

“We prayed, we talked to people, we gathered information, and we eventually decided that this was the way we were going to go,” her husband added.

Within six months, the team at Children’s Hospital of Philadelphia and Penn Medicine, along with their partners, created a therapy designed to correct KJ’s faulty gene. They used CRISPR, the gene editing tool that won its inventors the Nobel Prize in 2020. Instead of cutting the DNA strand like the first CRISPR approaches, doctors employed a technique that flips the mutated DNA “letter” — also known as a base — to the correct type. Known as “base editing,” it reduces the risk of unintended genetic changes.

In February, KJ got his first IV infusion with the gene editing therapy, delivered through tiny fatty droplets called lipid nanoparticles that are taken up by liver cells.

While the room was abuzz with excitement that day, “he slept through the entire thing,” recalled study author Dr. Rebecca Ahrens-Nicklas, a gene therapy expert at CHOP.

After follow-up doses in March and April, KJ has been able to eat more normally and has recovered well from illnesses like colds, which can strain the body and exacerbate symptoms of CPS1. The 9 ½-month old also takes less medication.

Still, researchers caution that it’s only been a few months. They’ll need to watch him for years.

“We’re still very much in the early stages of understanding what this medication may have done for KJ,” Ahrens-Nicklas said. “But every day, he’s showing us signs that he’s growing and thriving.”

Researchers hope what they learn from KJ will help other rare disease patients.

Gene therapies, which can be extremely expensive to develop, generally target more common disorders in part for simple financial reasons: more patients mean potentially more sales, which can help pay the development costs and generate more profit. The first CRISPR therapy approved by the U.S. Food and Drug Administration, for example, treats sickle cell disease, a painful blood disorder affecting millions worldwide.

“As we get better and better at making these therapies and shorten the time frame even more, economies of scale will kick in and I would expect the costs to come down,” Musunuru said.

Scientists also won’t have to redo all the initial work every time they create a customized therapy, Bhoopalan said, so this research “sets the stage” for treating other rare conditions.

Carlos Moraes, a neurology professor at the University of Miami who wasn’t involved with the study, said research like this opens the door to more advances.