VIP and autism: Furthermore, VIP interneuron impairment promotes in vivo circuit dysfunction in the cerebral cortex and autism-related behaviors in Dravet syndrome, a disease caused by mutation of the gene coding for voltage-gated sodium channel subunit Nav1.1, and in Rett syndrome, associated with mutations in the gene coding for methyl-CpG binding protein 2 (MECP2) located on the X chromosome, and both associated with recurrent seizures that ultimately lead to epilepsy [31].