Fragile X Syndrome

Snapshot

A 3-year-old boy is brought to a pediatrician. His past medical history is unknown, as this is his first visit to the pediatrician. His mother reports that the family prefers an isolated existence and therefore has not sought medical help. However, she reports being concerned about his learning abilities, as his speech appears delayed compared to his sisters. On physical exam, the boy has a prominently long face, large jaw, and large ears. The pediatrician recommends a genetic test.

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
- risk factors
  - family history
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
Prognosis
life span is normal

Presentation

Imaging

Studies

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

Complications