Fragile X Syndrome

Fragile X syndrome is a genetic condition that involves complications in the part of X chromosome. It is the commonest form of inherited intellectual disability (mental retardation) in boys.


Causes, incidence, and risk factors


Fragile X syndrome is caused by a change in a gene called FMR1. A small part of the gene code is repeated on a fragile area of the X chromosome. The more repeats, the more likely there is to be a problem.


The FMR1 gene makes a protein needed for your brain to grow properly. A defect in the gene makes your body produce too little of the protein, or none at all.


Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X is likely to affect them more severely. You can have Fragile X syndrome even if your parents do not have it. Usually females are the carriers of this Fragile X chromosome.




Behavior symptoms associated with fragile X syndrome includes


  • Delay in crawling, walking, or twisting
  • Hand clapping or hand biting
  • Hyperactive or impulsive behavior
  • Mental retardation
  • Speech and language delay
  • Tendency to avoid eye contact

Physical signs may include


  • Flat feet
  • Flexible joints and low muscle tone
  • Large body size
  • Large forehead or ears with a prominent jaw
  • Long face
  • Soft skin


Some of these problems are present at birth, while others may not develop until after puberty.

Signs and Symptoms

There are very few outward signs of Fragile X syndrome in babies. Some signs may include


  • Large head circumference in babies
  • Mental retardation
  • Large testicles after the start of puberty
  • Subtle differences in face features
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