In this study we analysed whether FXS could be caused by an alteration of NO metabolism, by studying the activation of the NF-κB-p65 subunit, the most abundant activated form in the nucleus, and also 3-nitrotyrosine and NO level, together with NOS isoform proteins detection in different brain areas from Fmr1-KO compared with wild-types of different ages. This evidence concerns the gene NFKB1 and fragile X syndrome.