Base editors can correct disease-causing genetic variants. 

After a neonate had received a diagnosis of severe carbamoyl-phosphate synthetase 1 deficiency, a disease with an estimated 50% mortality in early infancy, we immediately began to develop a customized lipid nanoparticle–delivered base-editing therapy. 

After regulatory approval had been obtained for the therapy, the patient received two infusions at approximately 7 and 8 months of age. 

In the 7 weeks after the initial infusion, the patient was able to receive an increased amount of dietary protein and a reduced dose of a nitrogen-scavenger medication to half the starting dose, without unacceptable adverse events and despite viral illnesses. 

No serious adverse events occurred. 

Longer follow-up is warranted to assess safety and efficacy.

N Engl J Med. 2025 May 15.

https://www.nejm.org/doi/full/10.1056/NEJMoa2504747