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4d ago

First Personalized CRISPR Therapy Successfully Treats Infant’s Rare Genetic Disorder

A custom gene-editing treatment developed in just six months corrected a fatal mutation in a baby, marking a breakthrough for rare disease therapies.

Baby KJ is held by one of his doctors, Rebecca Ahrens-Nicklas of the Children's Hospital of Philadelphia, as Kiran Musunuru of the University of Pennsylvania looks on.
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KJ Muldoon, who received a custom CRISPR edit to his genome, shown in spring 2025.
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Overview

  • KJ Muldoon, diagnosed with severe CPS1 deficiency shortly after birth, received a bespoke CRISPR therapy targeting his specific genetic mutation.
  • The therapy, developed by Children’s Hospital of Philadelphia and Penn Medicine, was fast-tracked by the FDA and administered in three doses between February and April 2025.
  • KJ has shown significant improvements, including normalized ammonia metabolism, better protein tolerance, and recovery from common illnesses without serious side effects.
  • The case, detailed in the New England Journal of Medicine, demonstrates the potential of personalized gene editing to treat ultra-rare diseases with no existing curative options.
  • Experts view this proof-of-concept as a foundation for expanding tailored CRISPR therapies to address other rare genetic disorders in the future.