The clinical relevance of this developmental shift is supported by the observations that KCC2 and NKCC1 expression levels are altered in several neurodevelopmental disorders associated with epilepsy (Aronica et al., 2007) and that mutations in the SLC12A5 gene, which encodes KCC2, are associated with autism spectrum disorder and schizophrenia (Merner et al., 2015), two disorders of neuronal development (see also Cherubini et al., 2022). Here, SLC12A5 is linked to schizophrenia.