A retrospective cohort study of Libmeldy (atidarsagene autotemcel) for MLD: What we have accomplished and what opportunities lie ahead.

Metachromatic leukodystrophy (MLD) results from ARSA gene mutations. Affected individuals meet early milestones before neurological deterioration and early death. Atidarsagene autotemcel (arsa-cel), an autologous haematopoietic stem cell gene therapy (HSC-GT) product, has demonstrated sustained clinical benefits in MLD. Arsa-cel was approved for NHS treatment in February 2022 for asymptomatic late infantile or early juvenile disease, or early symptomatic early juvenile MLD. We evaluate the impact of this approval in the largest real-world dataset of MLD HSC-GT. Hospital records were reviewed for all patients referred for NHS treatment following arsa-cel approval. Information was gathered about disease phenotype, presentation, eligibility, and affected siblings. In the year following NHS approval, 17 UK MLD patients were referred for treatment. Four patients met eligibility criteria and have been treated, including 1 infant who weighed 5 kg at leukapheresis. Eleven patients failed screening: 10 symptomatic patients with late infantile disease and 1 with early juvenile disease and cognitive decline. Two further patients with later onset subtypes did not meet the approval criteria. Three out of four treated patients were diagnosed by screening after MLD was diagnosed in a symptomatic older sibling. The success of HSC-GT for MLD has heralded a new era of hope for families affected by this devastating disease, yet currently, most patients are ineligible for treatment at diagnosis. The feasibility of apheresis in infants and the availability of a licenced, effective HSC-GT product highlights the urgent need for newborn screening to ensure that patients can be diagnosed and treated before symptom onset.