Fragile X syndrome (FXS) is an inherited disorder that causes intellectual disability, behavioral challenges and various physical characteristics. Though FXS occurs in both genders, males are more frequently affected than females, and generally with greater severity. Most males and some females with fragile X syndrome have characteristic physical features that become more apparent with age. These features include a long and narrow face, large ears, a large jaw and forehead, unusually flexible fingers, flat feet, and in males, enlarged testicles after puberty. The degree of intellectual disability and type of behavioral challenges varies from person to person. No specific treatment is available. Life expectancy is unaffected by FXS. FXS is caused by an expansion of repetitive repeat region of the FMR1 gene.