Cause

• Most cases of triple X syndrome are caused by an error in the egg or sperm cell formation---called nondisjunction. In others, the extra chromosome appears early in the embryo's development---called the mosaic form of triple X syndrome.
  
  

Significance

• In the nondisjunction form of Triple X, each cell in the body has the extra chromosome. In the mosaic form, only some cells have the extra chromosome. Many girls have no symptoms or very mild ones; symptoms usually are more pronounced in the nondisjunction type.
  
  

Physical Symptoms

• Physical symptoms of Triple X can include tall stature, an abnormally-small head and vertical skin folds covering the inner corners of the eyes.
  
  

Additional Symptoms

• A girl affected by Triple X may have learning disabilities and developmental delays involving motor skills, speech and language. She may have difficulty with interpersonal relationships. Most girls with Triple X have normal intelligence but may test lower than siblings.
  
  

Treatment

• Since no treatment is available to resolve the chromosomal abnormality, girls with symptoms should be treated as any child with a developmental disability at that level of severity.