Fragile X syndrome
| Fragile X syndrome | |
|---|---|
| Synonyms | Martin-Bell syndrome, Escalante syndrome |
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| Boy with fragile X syndrome | |
| Classification and external resources | |
| Specialty | Medical genetics, pediatrics, psychiatry |
| ICD-10 | Q99.2 |
| ICD-9-CM | 759.83 |
| OMIM | 300624 |
| DiseasesDB | 4973 |
| MedlinePlus | 001668 |
| eMedicine | ped/800 |
| Patient UK | Fragile X syndrome |
| MeSH | D005600 |
| Orphanet | 908 |
Fragile X syndrome (FXS) is a genetic disorder. Symptoms often include mild to moderate intellectual disability. Physical features may include a long and narrow face, large ears, flexible fingers, and large testicles. About a third of people 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.
Fragile X syndrome is typically due to the expansion of the CGG triplet repeat within the Fragile X mental retardation 1 (FMR1) gene on the X chromosome. This results in a failure to express the fragile X mental retardation protein (FMRP), which is required for normal neural development. Depending on the length of the CGG repeat, an allele may be classified as normal (unaffected by the syndrome), a premutation (at risk of fragile X associated disorders), or full mutation (usually affected by the syndrome). A diagnosis of fragile X syndrome is made through genetic testing to determine the number of CGG repeats. Testing for premutation carriers may allow for genetic counseling.
There is no medication that has a benefit specifically for fragile X syndrome. Medications are commonly used to treat symptoms of attention deficit and hyperactivity, anxiety, and aggression. Supportive management is important in optimizing functioning in individuals with fragile X syndrome, and may involve speech therapy, occupational therapy, and individualized educational and behavioral programs. Early intervention is recommended as it provides the most opportunity for developing a full range of skills. These interventions include education and medications with accompanied therapies.
Fragile X syndrome occurs in about 1 in 4,000 males and 1 in 8,000 females. The first complete DNA sequence of the repeat expansion in someone with the full mutation was generated by scientists in 2012 using SMRT sequencing.
Most young children do not show any physical signs of FXS. It is not until puberty that physical features of FXS begin to develop. Aside from intellectual disability, prominent characteristics of the syndrome may include an elongated face, large or protruding ears, flat feet, larger testes (macroorchidism), and low muscle tone. Recurrent otitis media (middle ear infection) and sinusitis is common during early childhood. Speech may be cluttered or nervous. Behavioral characteristics may include stereotypic movements (e.g., hand-flapping) and atypical social development, particularly shyness, limited eye contact, memory problems, and difficulty with face encoding. Some individuals with fragile X syndrome also meet the diagnostic criteria for autism.
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