STXBP1 and Encephalopathy: Among this growing list of synaptic vesicle cycle disorders, the most frequent is STXBP1 encephalopathy caused by de novo heterozygous pathogenic variants in syntaxin-binding protein 1 (STXBP1, also known as MUNC18-1;Verhage and Sørensen, 2020;John et al., 2021).