FMR1 and fragile X syndrome: FXS is caused by a mutation of the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene (FMR1 Fragile X Messenger Ribonucleoprotein 1 [Homo Sapiens (Human)]—Gene—NCBI, n.d.), leading to a deficit in the Fragile X Mental Retardation Protein (FMRP) [3].