SYN1 and Neurodevelopmental delay: Missense and truncation mutations in the SYN1 and SYN2 genes encoding Synapsin 1 and Synapsin 2 have both been associated with NDD with or without epilepsy (Fassio et al., 2011; Lignani et al., 2013; Peron, Baratang, Canevini, Campeau, & Vignoli, 2018).