Fragile X syndrome
... Symptoms of fragile X include: • mental impairment, ranging from learning disabilities to mental retardation • attention deficit and hyperactivity • anxiety and unstable mood • autistic-like behaviors • long face, large ears, flat feet, and • hyperextensible joints, especially fingers • Seizures (epilepsy) affect about 25% of people with fragile X Boys are typically more severely affected than girls. ... What Causes Fragile X? In 1991, scientists discovered the gene (called FMR1) that causes fragile X. In individuals who have fragile X syndrome, a defect in FMR1 (a "full mutation") shuts the gene down. ... Fragile X is inherited. ... The fragile X premutation can be passed silently down through generations in a family before a child is affected by the syndrome. Genetic Cause of Fragile X The FMR1 gene is located on the long arm of the X chromosome. ... Although a person who carries the premutation does not typically have symptoms of fragile X, the stretch of DNA is prone to further expansion when it is passed from a woman to her children. ... A male who inherits a full mutation exhibits characteristics of fragile X syndrome because his only X chromosome contains the mutated gene. A female may not be as severely affected as a male because each cell of her body needs to use only one of its two X chromosomes and randomly inactivates the other. How is Fragile X inherited? ... The remaining two chromosomes are called the sex chromosomes (X and Y).