ARHGEF9 and hereditary hyperekplexia: The current understanding of human startle disease (hyperekplexia) is based on mutations in genes encoding glycine receptor subunits (GLRA1, GLRB), the glycine transporter GlyT2 (SLC6A5) as well as in rare cases the synaptic scaffolding proteins collybistin (ARHGEF9) and gephyrin (GPHN) that lead to significant muscle hypertonia and neonatal apnea episodes (Rees et al., 2002, 2003, 2006; Harvey et al., 2004; Chung et al., 2013; Bode and Lynch, 2014; Schaefer et al., 2022).