Fragile X Syndrome

Fragile X syndrome is a genetic disorder caused by an expansion of a repeated DNA sequence within the FMR1 gene on the X chromosome, which silences the gene and eliminates the protein it normally produces, a protein needed for typical brain development. It is the most common inherited cause of intellectual disability and the most common known single-gene cause of autism spectrum disorder, with affected individuals often also showing large ears, a long face, and anxiety or attention difficulties. The condition takes its name from a fragile-appearing constriction on the X chromosome first observed under the microscope in the 1960s and 1970s, before the FMR1 gene itself was identified in 1991.