STXBP1 and epilepsy: First, the overall phenotypic spectrum of STXBP1-related disorders is broad, including a wide range of epilepsy presentations and neurological features.3,22–27 Second, no clear genotype–phenotype correlations have been identified to date.2 Third, as STXBP1 encodes for a synaptic protein, the pathogenic mechanism linking impaired release of synaptic vesicles to neurological features is less clear than, for example, ion channel-related disorders.