PCDH11X and schizophrenia: Non-clustered protocadherins are essential for nervous system development, as mutations in these genes have been linked to autism (Marshall et al., 2008; Morrow et al., 2008; Piton et al., 2011; Butler et al., 2015), schizophrenia (Gregório et al., 2009), intellectual disability (Kasnauskiene et al., 2012), microcephaly (Aran et al., 2016), and epilepsy (Dibbens et al., 2008; Lal et al., 2015).