Life\u2019s ability to successfully copy three billion distinct letters in the human genome<\/a> is an absolute biological wonder\u2014but sometimes, mistakes are made. Whether inherited or formed in utero, genetic disorders and other birth defects are common, and occur in one in every 33 babies in the U.S., according to the Centers of Disease Control and Prevention<\/a> (CDC). For all of human history, a person born with such a disorder likely had to live with the condition, and depending on the defect, those lives could be brutally short. <\/p>\n But in 2025, human history changed forever. <\/p>\n In a groundbreaking announcement, detailed in a study published in the New England Journal of Medicine<\/a>, scientists, doctors, and specialists from institutions around the U.S.\u2014including the Children\u2019s Hospital of Philadelphia, University of California-Berkeley, and Penn Medicine\u2014successfully saved the life of a newborn patient named KJ, who had been born with a rare genetic disorder. To pull off this incredible medical feat, doctors employed the world\u2019s first custom in vivo (i.e. inside a living organism, rather than in a petri dish) CRISPR gene therapy<\/a>. This technique, developed over decades thanks to U.S.-funded medical research, could help alleviate painful lives for millions of people born every year with now-fixable genetic disorders. <\/p>\n Related Story<\/p>\n \u201cYears and years of progress in gene editing<\/a> and collaboration between researchers and clinicians made this moment possible, and while KJ is just one patient, we hope he is the first of many to benefit from a methodology that can be scaled to fit an individual patient\u2019s needs,\u201d Children\u2019s Hospital of Philadelphia\u2019s Rebecca Ahrens-Nicklas, a co-author of the study, said in a press statement<\/a>.<\/p>\n The details of this incredible medical intervention play out like a made-for-tv medical drama, but the stakes were incredibly real and deadly serious. A week after his birth, doctors noticed something wasn\u2019t quite right with KJ. After ruling out a few possibilities, they stumbled across the unfortunate answer\u2014a rare genetic disorder called severe carbamoyl phosphate synthetase 1 (CPS1) deficiency that affects only one in every 1.3 million babies. This disorder inhibits the body\u2019s ability to get rid of ammonia<\/a>, a product of protein metabolism. This can have deadly consequences, impact brain development, and wreak havoc on the liver. Usually, the treatment for a disorder like this is a liver transplant, but that was not an option for the infant boy, who was still too young to be considered for the surgery.<\/p>\n So, once arriving at a diagnosis, Ahrens-Nicklas contacted a gene-editing specialist at the University of Pennsylvania named Kiran Musunuru and \u201cthe clock start[ed]in my mind,\u201d he later told The New York Times<\/a>. Working with a team of specialists across the country for six months, Ahrens-Nicklas and Musunuru developed a targeted gene therapy to fix KJ\u2019s specific variant of CPS1. Meanwhile, KJ was kept under medical surveillance at the hospital and subsisted on a diet completely devoid of protein<\/a> to avoid making his condition worse. By the time the CRISPR treatment was ready, KJ was in the 7th percentile for his weight. <\/p>\n On February 25, the team began administering the treatment<\/a>, with Ahrens-Nicklas and Musunuru describing the process as both exciting and terrifying. <\/p>\n Related Story<\/p>\n \u201cOne of the most terrifying moments was when I walked into the room and said, \u2018I don\u2019t know if it will work but I promise I will do everything I can to make sure it is safe,\u2019\u201d Ahrens-Nicklas told The New York Times. <\/p>\n The first infusion took two hours, and within two weeks, KJ began eating protein like a healthy baby. A second dose arrived 22 days later, and about two weeks ago, KJ received a third. Although it\u2019s unknown if he will eventually still need a liver transplant<\/a>, doctors can now safely say that a human life has been saved thanks to the world\u2019s first bespoke in vivo gene therapy\u2014a huge testament to decades of a research and experimentation. KJ is now at home with his family.<\/p>\n