Fragile X Syndrome Definition

An inherited genetic disorder that results in significant intellectual impairment. Fragile X syndrome arises from a monogenic (single-gene), increased repeat mutation affecting the FMR1 gene on the X chromosome and is the leading cause of inherited intellectual impairment in males. Fragile X syndrome more severely affects males because females have a second X chromosome that can somewhat override the mutated gene on the other X chromosome.

Most females are unaffected carriers. Because males have one X chromosome and one Y chromosome, they lack this dampening affect. A male can also be an unaffected carrier of the mutated gene, though this is very rare, and will thus pass the mutation to all of his daughters though none of his sons.

Symptoms of Fragile X Syndrome

The symptoms of fragile X syndrome vary in severity though typically include:

  • developmental delays
  • speech impairments
  • intellectual impairment (sometimes profound)
  • seizures
  • behavioral problems
  • AUTISM-like characteristics
  • physical features that may include overly flexible joints, flat feet, long facial configuration, and oversized ears

Diagnosis of Fragile X Syndrome and Treatment

Diagnosis occurs through genetic testing, typically cytogenic analysis. Treatment may include supportive measures such as special education in school, speech and language pathology, and medications to moderate behaviors and control seizures. Children who are mildly affected may require little extra care and may attend regular classes and schools; those who are severely affected may require ongoing support and institutional care.


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