What is fragile X syndrome - Medicine and Health

Fragile X syndrome is the most common cause of inherited mental retardation. Infants and toddlers with fragile X are likely to have delayed development of body movement (called motor skills) and delayed speech abilities. For instance, boys with fragile X walk and say their first words when they are about 20 months old; unaffected boys walk and talk at about 12 months. A child with fragile X may not learn words as quickly as other children of the same age do. The child may also have difficulty understanding instructions. Boys with fragile X have more severe problems compared to girls with the disease.

Children with fragile X syndrome typically have behavioral problems, such as temper tantrums and hyperactivity. In some cases, a child might show autism-like symptoms, such as poor eye contact with others.

Although children with fragile X usually do not have unusual physical characteristics as infants, such features might appear as they grow older. A school-aged child with fragile X might have a long face with a prominent jaw, prominent forehead or relatively large ears.

Gender plays a role in the symptoms and severity of fragile X. Boys with the syndrome have moderate or severe mental retardation, while girls with fragile X have milder mental retardation. Boys are also more likely to have the unusual facial features mentioned above.