Single nucleotide polymorphisms or abnormal expression of NTNG1 and NTNG2 are related to psychiatric disorders such as autism, Rett syndrome, schizophrenia, and bipolar disorder in human and murine models (Fukasawa et al., 2004; Aoki-Suzuki et al., 2005; Chuang et al., 2015; Huang and Hsueh, 2015; Heimer et al., 2020). Here, NTNG1 is linked to bipolar disorder.