In November 2025, the FDA introduced a new regulatory pathway called the "Plausible Mechanism Pathway" to allow the approval of personalized gene therapies for the treatment of ultra-rare genetic diseases[6]. This journey was inspired by the case of newborn KJ from Philadelphia, who became the first recipient of personalized gene-editing therapy to treat life-threatening liver disease[6]. The new regulatory pathway should enable the scaling of such drugs by formally approving them and enabling their reimbursement[6]. However, ethicists warn that this path could become a "Pandora's box" and raise concerns about its potential consequences[6]. Approval under this pathway could be based on data from a small number of patients, representing a significant shift from traditional clinical trials requiring large randomized trials[5]. The pathway is intended for diseases caused by a clearly defined genetic or molecular abnormality that the therapy directly targets[5].