STXBP1 and Nystagmus: Pathogenic variants of STXBP1 have been associated with EIEE4 (also known as Ohtahara syndrome), which is manifested as intractable epilepsy, severe developmental delay and mental retardation (Saitsu et al., 2008; Allen et al., 2016), while nystagmus was noted in a few cases (Stamberger et al., 2016).