Fragile X syndrome | |
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Other names | Martin–Bell syndrome,[1] Escalante syndrome |
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Boy with protruding ears characteristic of fragile X syndrome | |
Specialty | Medical genetics, pediatrics, psychiatry |
Symptoms | Intellectual disability, long and narrow face, large ears, flexible fingers, large testicles[1] |
Complications | Seizures[1] |
Usual onset | Noticeable by age 2[1] |
Duration | Lifelong[2] |
Causes | Genetic (X-linked dominant)[1] |
Diagnostic method | Genetic testing[2] |
Treatment | Supportive care, early interventions[2] |
Frequency | 1 in 4,000 (males), 1 in 8,000 (females)[1] |
Fragile X syndrome (FXS) is a genetic neurodevelopmental disorder characterized by mild-to-moderate intellectual disability.[1] The average IQ in males with FXS is under 55, while about two thirds of affected females are intellectually disabled.[3][4] Physical features may include a long and narrow face, large ears, flexible fingers, and large testicles.[1] About a third of those affected have features of autism such as problems with social interactions and delayed speech.[1] Hyperactivity is common, and seizures occur in about 10%.[1] Males are usually more affected than females.[1]
This disorder and finding of fragile X syndrome has an X-linked recessive inheritance.[1] 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.[1] 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.[1] Diagnosis requires genetic testing to determine the number of CGG repeats in the FMR1 gene.[5] Normally, there are between 5 and 40 repeats; fragile X syndrome occurs with more than 200.[1] 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.[1] Testing for premutation carriers may allow for genetic counseling.[5]
There is no cure.[2] Early intervention is recommended, as it provides the most opportunity for developing a full range of skills.[6] These interventions may include special education, speech therapy, physical therapy, or behavioral therapy.[2][7] Medications may be used to treat associated seizures, mood problems, aggressive behavior, or ADHD.[8] Fragile X syndrome tends to show more symptoms on affected males since females have another X chromosome which can compensate for the damaged one.[4][9]