by WKRC

Sun, December 21, 2025 at 4:45 PM

One-year-old KJ Muldoon, the first infant to undergo gene-editing therapy for a rare genetic disorder, is now taking his first steps. (CHOP)

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• Gene-editing
• CRISPR
• Therapy
• Carbamoyl phosphate synthetase 1 deficiency
• Children's Hospital of Philadelphia
• KJ Muldoon
• Genetic disorder
• Developmental milestones

PHILADELPHIA (WKRC) - One-year-old KJ Muldoon, the first infant to receive gene-editing therapy for a rare genetic disorder, is now taking his first steps, according to a Dec. 17 news release from Children’s Hospital of Philadelphia.

KJ was diagnosed shortly after birth in August 2024 with severe carbamoyl phosphate synthetase 1 deficiency, a rare metabolic condition that affects about 1 in 1.3 million babies and can be life-threatening. He spent the first 10 months of his life hospitalized.

His parents, Kyle and Nicole Muldoon, were connected with Dr. Rebecca Ahrens-Nicklas and Dr. Kiran Musunuru, who developed a customized treatment using CRISPR gene-editing technology.

“Years and years of progress in gene editing and collaboration between researchers and clinicians made this moment possible,” Ahrens-Nicklas said, according to PEOPLE.

KJ received three doses of the therapy without serious side effects and was discharged from the hospital in June.

Doctors say his condition has improved significantly and that he is developing well, though he will be monitored for life.

“The promise of gene therapy that we’ve heard about for decades is coming to fruition,” Musunuru said, according to PEOPLE.

KJ celebrated his first birthday at home in August and is now meeting developmental milestones, including cheering on the Philadelphia Eagles with his family.

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“Just to see him do these things that we never thought were possible has been inspiring,” Kyle Muldoon said, according to PEOPLE.