SLC6A4 and fragile X syndrome: Signal intensities in the dorsal lateral geniculate nucleus (dLGN) of the visual in Fmr1-KO mouse relay showed a tendency to decreased levels and the ratio of the SERT mRNA expression in dLGN to that in the ventrobasal nucleus (VB) of the somatosensory relay (90% of control, P < 0.048) was significantly reduced when compared with wild-type controls (Figures 4C,D) suggesting dysregulation of serotonin-dependent developmental processes in FXS.