Fragile X syndrome (FXS) is a genetic disorder characterized by mild-to-moderate intellectual disability. The average IQ in males with FXS is under 55, while about two thirds of affected females are intellectually disabled. Physical features may include a long and narrow face, large ears, flexible fingers, and large testicles. About a third of those affected have features of autism such as problems with social interactions and delayed speech. Hyperactivity is common, and seizures occur in about 10%. Males are usually more affected than females.
This disorder and finding of fragile X syndrome has an X-linked dominant inheritance. It is typically caused by an expansion of the CGG triplet repeat within the FMR1 (fragile X messenger ribonucleoprotein 1) gene on the X chromosome. This results in silencing (methylation) of this part of the gene and a deficiency of the resultant protein (FMRP), which is required for the normal development of connections between neurons. Diagnosis requires genetic testing to determine the number of CGG repeats in the FMR1 gene. Normally, there are between 5 and 40 repeats; fragile X syndrome occurs with more than 200. A premutation is said to be present when the gene has between 55 and 200 repeats; females with a premutation have an increased risk of having an affected child. Testing for premutation carriers may allow for genetic counseling.
There is no cure. Early intervention is recommended, as it provides the most opportunity for developing a full range of skills. These interventions may include special education, speech therapy, physical therapy, or behavioral therapy. Medications may be used to treat associated seizures, mood problems, aggressive behavior, or ADHD. Fragile X syndrome tends to show more symptoms on affected males since females have another X chromosome which can compensate for the damaged one.
Most young children do not show any physical signs of FXS. It is not until puberty that physical features of FXS begin to develop.
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Explores genetic traits inheritance, family tree analysis, and various modes of genetic trait transmission in humans, including specific genetic disorders.
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