VIP and fragile X syndrome: As the FXS field emphasizes dysfunctional inhibition as an underlying cause of many symptoms associated with FXS (and likely ASD), several studies have used animal models, particularly the Fmr1 KO mouse to examine the specific contribution of three major inhibitory cells: parvalbumin (PV+), somatostatin (SST+) and vasoactive Intestinal Peptide (VIP+).