FMR1 and autism: Fragile X syndrome (FXS), in which transcriptional silencing of the Fmr1 gene leads to loss of the fragile X mental retardation protein (FMRP), represents one of the most common single-gene cause of autism [from 1% to 6% of cases; (188)], and the vast majority of FXS individuals show tactile impairments (189).