Updated: 12/26/2021

McCune-Albright Syndrome

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  • Snapshot
    • A 6-year-old girl presents to the pediatrician with her mother due to the presence of vaginal bleeding. The mother said she began menarche at 14 years of age and the patient's older sister at 15. The mother is in a healthy relationship with her husband and reports that the patient has been complaining of bone pain and stiffness in her legs. On physical exam, the patient is happy, playful, and conversational. There is tenderness to palpation in her bilateral lower extremities, as well as a hyperpigmented spot with ragged edges. There is mild blood in the vaginal introitus with no evidence of vaginal trauma.
  • Introduction
    • Clinical definition
      • a rare genetic disorder characterized by
        • polyostotic fibrous dysplasia
        • café-au-lait spots
        • endocrinopathy
          • classically with precocious puberty
          • others include hyperthyroidism, infantile Cushing syndrome, gigantism, and acromegaly
  • Epidemiology
    • Incidence
      • precocious puberty is more common in females
    • Demographics
      • early childhood
  • Etiology
    • Pathogenesis
      • activating mutation in GNAS1 leads to overproduction of downstream proteins
    • Genetics
      • inheritance pattern
        • autosomal recessive
      • mutation
        • postzygotic somatic activating mutation in GNAS1 on chromosome 20
          • GNAS1 codes for a Gsα
            • involved in G-protein signaling
  • Presentation
    • Symptoms
      • precocious puberty
        • vaginal bleeding or breast development without pubic hair growth
          • typically occurs at an earlier age than normal
      • bone pain
      • joint stiffness
    • Physical exam
      • café-au-lait spots
        • no family history
      • pathologic fractures
      • visible bone deformities may be found
  • Imaging
    • Radiographs
      • indication
        • involved in the work-up of bone involvement (e.g., fracture)
      • findings
        • patchy areas of lytic bone lesions and sclerosis
          • more commonly in the metaphyseal and diaphyseal regions
        • trabeculated lesions with a ground-glass appearance may be found
  • Studies
    • Labs
      • molecular testing for GNAS1 analysis
  • Differential
    • Neurofibromatosis type I
      • has neurologic involvement and a family history of café-au-lait spots
  • Treatment
    • There are no specific treatments for McCune-Albright syndrome
      • treatment is aimed at the complications of this genetic disorder
  • Complications
    • Increased risk for fracture
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