Fragile X syndrome (FXS) is an inherited X-linked genetic disorder characterized by developmental, cognitive and mental impairment. FXS, also known as Martin-Bell syndrome or Marker X syndrome, is the most common form of inherited intellectual disability, with frequency and severity more prevalent in males compared to females. This disorder is caused by genetic defects in the Fragile X Mental Retardation 1 (FMR1) gene, responsible for making the protein necessary for normal cognitive development and female reproductive function. Affected people with FXS have normal life expectancy, but more care and support for them will be needed due to their impaired cognitive and intellectual development. They typically show delayed development in speech and language by the age of two. The severity of the symptoms can vary among individuals depending on gender and the type of genetic mutation. Apart from intellectual disability, affected individuals may also display behavioral problems, or have attention deficit disorder. Physical features such as a long face, large ears, prominent jaw and forehead are also characteristic for people with FXS. References: Fragile X-associated Disorders. National Fragile X Foundation Saul RA, Tarleton JC (1998, Updated 2012 Apr 26). FMR1-Related Disorders. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2016.