Abnormalities in the fragile X gene fall into two categories: those caused by the full mutation and those associated with the premutation.
The full mutation involves greater than 200 copies of a three-nucleotide sequence (CGG) in the FMR1 gene found on the X chromosome.Normal individuals typically have fewer than 40 repeats.
The premutation involves 55-200 CGG repeats in this gene. Individuals with the premutation are known as carriers and the children of female carriers are more likely to be born with the full mutation.
The full mutation of the FMR1 gene causes fragile X syndrome, for which there is no cure, but targeted treatments that may reverse this disorder are currently being tested at the MIND Institute. Without a normal copy of the fragile X gene, a vital protein is not made and the result is the onset of characteristic mental disorders, which can range from learning disabilities to severe cognitive or intellectual disabilities, such as autism.
In fact, 30 percent of boys with the fragile X mutation are diagnosed with autism. Fragile X syndrome is the most commonly known single-gene cause of autism, responsible for between 2 and 6 percent of autism cases.
In girls, the full mutation often manifests as shyness, math learning disability and social anxiety.
Treatment of the syndrome depends on its manifestations in the individual, and ranges from behavioral therapy to medication.
Last year, the Hagermans and their colleagues reported that the fragile X premutation may be twice as common as previously suspected, potentially affecting over one million men, women and children in the United States.
The premutation can cause attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder in children; primary ovarian failure (early menopause) in women; and FXTAS, or frag
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University of California - Davis - Health System