NOS1 and fragile X syndrome: Given the key role of NO in diverse neural processes including synaptic plasticity, retrograde signaling, development, excitotoxicity, and mental health (Brenman et al., 1996; Hölscher, 1997; Contestabile, 2000; Calabrese et al., 2007; Garthwaite, 2008; Steinert et al., 2010), the loss of NOS1 in the developing FXS neocortex may contribute to the pathophysiology of the disorder.