A 19-month-old girl in the UK has become the first child to receive a new gene therapy for metachromatic leukodystrophy (MLD), a fatal genetic disorder. The therapy, called Libmeldy, works by inserting a working copy of the faulty gene into the patient's stem cells, which are then used to produce healthy cells. The treatment has shown promise in clinical trials, with patients able to break down sulfatides at normal rates and showing typical patterns of motor development. The long-term effectiveness of the therapy is still being studied.