FMR1 (fragile X mental retardation 1) is a human gene that codes for a protein called fragile X mental retardation protein, or FMRP.This protein, most commonly found in the brain, is essential for normal cognitive development and female reproductive function.s a result, this part of the FMR1 gene is methylated, which silences the gene (it is turned off and does not make any protein). Without adequate FMRP, severe learning deficits or mental retardation can develop, along with physical abnormalities seen in fragile X syndrome.