Updated: 6/26/2017

Fragile X Syndrome

Review Topic
  • PhotoA 13-year-old boy is brought to his pediatrician. He is mentally retardarded, has a prominant jaw, and large soft ears, and large testicles. 
  • X-linked genetic abnormality
    • trinucleotide repeat (CGG) on FMR1 gene of the X-chromosome 
    • may show genetic anticipation, but family history of disease may not be present
      • anticipation is the expansion of the trinucleotide repeat in future generations resulting in more severe symptoms
    • caused by defect affecting the methylation and expression of the FMR1 gene
  • Epidemiology
    • second most common cause of mental retardation
    • most common cause of mental retardation in boys
  • Symptoms
    • symptoms and/or behavioral problems may develop at birth or afterwards
    • many children experience exacerbation of such problems during puberty, as mentioned below
  • Physical exam
    • behavior problems may be evident including
      • delay in movement (i.e. crawling, ambulation,rolling)
      • hyperactive behavior (impulsive, repetitive, ritualistic)
      • signs of mental retardation and/or disability
      • autism spectrum disorder (speech and language disorders)
    • physical signs indicative of syndrome may be evident including 
      • flattened feet
      • flexible joints
      • low muscle tone
      • enlarged body habitus
      • enlarged, elongated foreheads, long face
      • low-set and/or enlarged ears
      • pectus excavitatum  
      • soft skin
      • macro-orchidism (enlarged testicles)
      • mitral valve prolapse
  • Diagnosis is based primarily on clinical observation and family history
  • Head circumference
    • may be larger than average at birth
  • Genetic studies
    • may confirm Fragile X syndrome
    • number of gene repeats can provide insight into anticipating severity of disease
  •  Cerebral palsy, Down syndrome, other syndromic disorders
  • Medical management
    • there are no specific treatments for Fragile X syndrome
    • special education and training
      • indicated in all cases to achieve highest level of function possible
Prognosis, Prevention, and Complications
  • Prognosis
    • ranges widely and depends highly on the level of mental disabilty/retardation
  • Prevention
    • there are no preventive measures for this disorder
    • genetic counseling could be of value for reproductive health
  • Complications
    • recurrent infections, seizure disorders, and potentially autism, though not in all cases



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