Just a year ago, the case of a baby, K.J. Muldon, who suffered from a rare genetic metabolic disease –which can cause irreversible and fatal neurodegeneration– and was cured thanks to personalized gene therapy. A pioneering example of so-called n=1 therapy, that is, a therapy specifically created to treat a specific mutation present in only one patient. This success story was considered one of the great scientific achievements of 2025, and filled many parents with hope for their children affected by very serious rare diseases without treatment.