As a matter of fact, in a pilot study, we have reported that nearly 80% of children and adolescents diagnosed with ADHD had a genetic DAO deficit, and in nearly 20% this deficit was severe (https://www.aepap.org/sites/default/files/documento/archivos-adjuntos/878-texto_del_articulo-3110-2-10-20220623.pdf accessed on 1 Augutst 2023). Here, DAO is linked to attention deficit-hyperactivity disorder.