The fragile X syndrome is the most common form of inherited mental retardation in humans, caused by an expansion of the cytosine-guanine-guanine (CGG) repeat in the fragile X mental retardation 1 (FMR1) gene located on the X chromosome. Antibody tests have been developed to identify fragile X patients, based on the presence or absence of fragile mental retardation protein (FMRP) in both lymphoc…