Fragile X Syndrome (FXS)
Fragile X Syndrome (FXS) is a genetic disorder caused by a mutation (a change in the DNA structure) in the X chromosome. It results in a wide range of developmental, physical and behavioral problems and is the most common known cause of inherited developmental disability worldwide.
One in 2,500 males and one in 5,000 females are affected. One in 250 females carries the premutation and will pass the gene on to 50% of her offspring, male or female. Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X is likely to affect them more severely.
You can have fragile X syndrome even if your parents do not have it; a family history of fragile X syndrome, developmental problems, or intellectual disability may not be present.
The genetic disorder is a mutation in a gene on the ‘X’ chromosome called FMR1 (fragile X mental retardation gene 1). This gene normally contains a repeat code of 6 – 50 ‘CGG’ triplet repeats. Premutation carriers have a small change in the FMR1 gene (a repeat code of 50 –200), whereas the full mutation tends to be affected individuals with a large change in the gene (more than 200 repeats). The mutation turns the gene off, thus causing the problems associated with the syndrome.
Features usually include:
- intellectual disabilities, ranging from mild learning disabilities to more severe intellectual impact
- attention deficit and hyperactivity, particularly in young children
- anxiety and unstable mood
- autistic behaviors and is the most common known genetic (“single gene”) cause of autism
- sensory integration problems, such as hypersensitivity to loud noises or bright lights
- speech delay, with expressive language more severely affected than receptive language.
- seizures (epilepsy) affect about 25% of people with Fragile X
FXS is part of a family of genetic conditions known as Fragile X-associated disorders (FXD). Other conditions include Fragile X-associated tremor/ataxia syndrome (FXTAS), Fragile X-associated primary ovarian insufficiency (FXPOI), and Fragile X-Associated Neuropsychiatric Disorders (FXAND).