Turner Syndrome

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Basics

Description

  • Turner syndrome (TS) is a condition characterized by ovarian dysgenesis and short stature in phenotypic females who have only one sex chromosome, an X, although a partial second sex chromosome, X or Y, may be present.
  • The most common sex chromosome abnormality syndrome in females
  • System(s) affected: cardiovascular; reproductive; endocrine/metabolic; musculoskeletal; nervous; renal/urologic
  • Synonym(s): Ullrich-Turner syndrome; Bonnevie-Ullrich syndrome; monosomy X; sexual infantilism; gonadal dysgenesis

Epidemiology

Incidence
  • Occurs in 1/2,500 live female births
  • ~1–3% of all conceptuses affected, of whom <1% will survive to term; accounts for 15% of all spontaneously aborted fetuses
  • Predominant sex: female only

Prevalence
Estimated 50,000 to 75,000 females in the United States

Etiology and Pathophysiology

  • Haploinsufficiency of short stature homeobox-containing gene (SHOX), located in the pseudoautosomal region of the X chromosome, is thought to be responsible for short stature and skeletal abnormalities in TS.
  • Monosomy for all or part of the X chromosome can result in features of TS; genes located mainly in Xp11.2–p22.1

Genetics
  • 50% of patients have 45,X karyotype (sporadic nondisjunction). Translocations involving the X chromosome may result in TS.
  • 80% of girls with 45,X have maternal X, although phenotype is identical if X is paternal.
  • TS occurs with a deletion of the SRY segment of the Y chromosome in 46,XY karyotype, with resulting female phenotype (5–6%).
  • FISH or PCR may be necessary to identify Y material because of increased risk of gonadoblastoma (7–10%) if Y material is present; indicated if signs of virilization or marker chromosome present
  • Also may be mosaic for 45,X/46,XY, 45,X/46,XX, or 45,X/47,XXX

Commonly Associated Conditions

  • Gonadal dysgenesis (infertility 98%)
  • Short stature (100%), usually not growth hormone (GH)-deficient. Height is generally 20 cm below that expected for family.
  • Hearing loss (50%), otitis media (70–100%)
  • Frequent (>5–10% but <50% of individuals)
    • Cardiovascular abnormalities, including coarctation of the aorta (15–30%), aortic valvular disease (1/3 have bicuspid aortic valve), mitral valve prolapse (25%), aortic root dilatation (8–29%), aortic dissection, electrocardiogram (ECG) abnormalities
    • Bicuspid aortic valve or left-sided obstructive lesion in a female fetus or child should prompt a genetic evaluation for TS (1)[C].
    • Renal abnormalities
    • Hypertension (HTN; >30%)
    • Glucose intolerance
    • Hyperlipidemia
    • Ocular abnormalities
    • Hypothyroidism, autoimmune thyroiditis
    • GI vascular malformations
    • Glucose intolerance
    • Gonadoblastoma in 8% of individuals with Y chromosomal material
  • Occasional: inflammatory bowel disease, celiac disease, colon cancer, neuroblastoma, juvenile rheumatoid arthritis, liver disease (especially cirrhosis)

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