Updated: 12/24/2021

Fragile X Syndrome

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  • Snapshot
    • A 4-year-old girl is brought to the pediatrician for evaluation of learning issues. Her mother reports that there is a family history of intellectual disability in the men in her family, but she is unsure what that syndrome is. On physical exam, the patient has a mildly long face and slightly prominent ears. Tests show that her speech and language skills are delayed for her age. She is referred to speech and language therapist as well as genetic testing for suspected fragile X syndrome.
  • Introduction
    • Overview
      • fragile X syndrome is an X-linked dominant disorder characterized by macroorchidism, characteristic facial features, intellectual disability, and miral valve prolapse, caused by trinucleotide repeat (CGG) on the FMR1 gene
  • Epidemiology
    • Incidence
      • the most common cause of inherited intellectual disability
    • Demographics
      • females have less impairment and less physical features typical of fragile X syndrome
      • male > female
    • Risk factors
      • family history
  • ETIOLOGY
    • Genetics
      • inheritance pattern
        • X-linked dominant inheritance with variable penetrance
      • mutations
        • gene
          • trinucleotide repeat in FMR1 gene resulting in decreased expression
            • CGG repeats
    • Associated conditions
      • medical conditions and comorbidities
        • mitral valve prolapse
        • gastroesophageal reflux disease
  • Presentation
    • Symptoms
      • common symptoms
        • symptoms and behavioral problems may develop at birth of afterwards
        • characterized by developmental, cognitive, and neuropsychiatric issues
      • developmental
        • developmental delay in motor, speech, and language skills
      • cognitive
        • low IQ
      • neuropsychiatric
        • autism-like behaviors
          • hand flapping
          • avoidance of eye contact
        • anxiety
        • behavioral issues
          • aggression
          • attention deficits
          • oppositional
          • tantrums
      • seizure disorders
    • Physical exam
      • inspection
        • facial features
          • long face
          • large jaw
          • large everted ears
        • pectus excavatum
        • scoliosis
        • protruding chin
        • post-pubertal macroorchidism
        • hyperextensible joints
        • heart murmur or click
          • mitral valve prolapse
  • Imaging
    • Radiograph
      • indications
        • evaluate for scoliosis
      • findings
        • scoliosis
    • Echocardiograph
      • indications
        • evaluate for mitral valve prolapse
      • findings
        • mitral valve prolapse
  • Studies
    • DNA testing is diagnostic
      • Southern blot test
      • polymerase chain reaction
  • Differential
    • Autism spectrum disorder (ASD)
      • key distinguishing factor
        • similar behaviors such as hand flapping and avoidance of eye contact
        • patients with ASD lacks physical features typical of fragile X syndrome
  • Treatment
    • Treatment is aimed at symptomatic management
    • Lifestyle
      • specialist therapists
        • indications
          • speech and language therapy
          • occupational therapy
          • physical therapy
          • behavioral therapy
    • Medical
      • proton pump inhibitors
        • indications
          • gastroesophageal reflux disease
  • Complications
    • Recurrent infections
    • Seizure disorders
  • Prognosis
    • Life span is normal

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(M2.PD.15.0) A 4-year-old boy presents to his pediatrician for severe developmental delay. On exam he is noted to have macroorchidism, hypertelorism, large protruding ears, a large jaw, and a long thin face. Suspicious of what the diagnosis may be, the pediatrician orders a PCR and DNA sequencing. The results reveal an expansion of 250 repeats of CGG. What is the diagnosis of the boy?

QID: 106975
1

Huntington's disease

5%

(4/84)

2

Fragile X syndrome

88%

(74/84)

3

Freidrich ataxia

5%

(4/84)

4

Myotonic dystrophy type 1

1%

(1/84)

5

Spinal and bulbar muscular atrophy

0%

(0/84)

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