Since then, two more in vivo AAV gene therapies have been approved by EMA and the United States Food and Drug Administration (FDA): Luxturna and Zolgensma (Keeler and Flotte, 2019), with Upstaza for aromatic L-amino acid decarboxylase deficiency and Roctavian for Haemophilia A having also secured marketing authorisations from EMA (BioMarin Investors, 2022; PTC Therapeutics, 2022). This evidence concerns the gene DDC and hyperinsulinemic hypoglycemia, familial, 4.