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Turner syndrome

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Here is a comprehensive overview of Turner syndrome drawn from authoritative medical textbooks.

Turner Syndrome

Definition & Epidemiology

Turner syndrome results from complete or partial monosomy of the X chromosome and is characterized by hypogonadism in phenotypic females. It is the most common sex chromosome abnormality in females, affecting approximately 1 in 2,000–3,000 live-born females. Notably, the 45,X karyotype is the single most common cytogenetic abnormality found in spontaneously aborted fetuses, accounting for ~18% of chromosomally abnormal abortions — only about 1% of 45,X embryos survive to birth.
— Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 168

Karyotypes

TypeFrequencyDetails
Classic 45,X~57%Complete absence of one X chromosome
Structural abnormalities~14%Isochromosome Xq [46,X,i(Xq)], ring X [46,X,r(X)], deletions Xp or Xq
Mosaics~29%45,X/46,XX; 45,X/46,XY; 45,X/47,XXX; etc.
Key point on mosaicism: With sensitive molecular techniques, mosaicism may be detected in up to 75% of cases. Patients with a high proportion of 45,X cells have more severe phenotypes; those with readily detectable 45,X/46,XX mosaicism may appear nearly normal and present only with primary amenorrhea.
Y chromosome sequences: 5–10% of patients carry Y chromosome sequences (full 45,X/46,XY or translocated Y fragments), placing them at significantly higher risk for gonadoblastoma.
— Robbins & Kumar Basic Pathology, p. (block 1)

Clinical Features

Clinical features and karyotypes of Turner syndrome — showing short stature, low posterior hairline, webbed neck, broad chest with widely spaced nipples, coarctation of aorta, cubitus valgus, streak ovaries, peripheral lymphedema at birth, and pigmented nevi

Neonatal / Infantile Presentation

  • Peripheral lymphedema of hands and feet (lymph stasis)
  • Swelling of the nape of the neck → cystic hygroma → resolves to leave neck webbing and loose posterior neck skin
  • Congenital heart disease in 25–50%:
    • Preductal coarctation of the aorta (most common)
    • Bicuspid aortic valve
    • Aortic root dilation (~30%); 100-fold increased risk of aortic dissection
    • Cardiovascular disease is the leading cause of death in childhood

Childhood / Adolescent Features

  • Short stature (rarely exceeds 150 cm) — below 3rd percentile
  • Low posterior hairline
  • Webbing of the neck (pterygium colli)
  • Cubitus valgus (increased carrying angle of arms)
  • Shield-shaped chest with widely spaced nipples
  • High-arched palate
  • Renal anomalies: horseshoe kidney
  • Failure to develop secondary sex characteristics at puberty
  • Genitalia remain infantile; minimal breast development; scant pubic hair
  • Primary amenorrhea — Turner syndrome accounts for ~one-third of all primary amenorrhea cases
  • Pigmented nevi

Reproductive / Endocrine

  • Streak ovaries: normal fetal ovarian development up to ~18 weeks, then accelerated oocyte loss — complete by age 2 years. The ovaries are replaced by fibrous strands devoid of follicles and oocytes ("menopause before menarche")
  • Infertility in the vast majority; a very small number of mosaic patients can conceive
  • ~50% develop autoimmune thyroiditis with clinical hypothyroidism (especially those with isochromosome Xq)
  • Subset develops glucose intolerance, obesity, insulin resistance, non-alcoholic fatty liver disease — some fulfill criteria for metabolic syndrome

Cognitive Profile

  • Intelligence generally within normal limits
  • Subtle deficits in non-verbal, visual-spatial information processing
  • Some observations suggest that the parent-of-origin of the single X chromosome influences social adaptation
— Robbins, Cotran & Kumar, p. 168–169

Pathogenesis

  • In ~80% of cases the retained X chromosome is maternal in origin — the error occurs in paternal gametogenesis (sperm)
  • Key gene: SHOX (short stature homeobox gene) at Xp22.33, located in the pseudoautosomal region — escapes X inactivation, so normally two copies exist in both sexes. Haploinsufficiency of SHOX causes short stature (SHOX deletions are also found in 2–5% of otherwise normal children with short stature)
  • Genes on the short arm predominantly determine somatic features; genes on the long arm affect fertility and menstruation
  • Loss of one copy of genes in the pseudoautosomal region (shared by X and Y, normally escaping X inactivation) contributes to many features
— Robbins, Cotran & Kumar, p. 169

Diagnosis

  • Karyotyping is the gold standard
  • Prenatal diagnosis: possible via fetal karyotyping (amniocentesis or CVS)
  • Clinical suspicion in adults: combination of short stature + primary amenorrhea
  • ~5% of young females diagnosed with coarctation of the aorta have Turner syndrome

Management Highlights

IssueManagement
Short statureGrowth hormone therapy (note: worsens insulin resistance)
Hypogonadism / amenorrheaEstrogen + progesterone hormone replacement therapy
CardiovascularRegular cardiac imaging; monitor for aortic dilation/dissection
ThyroidScreen for and treat autoimmune hypothyroidism
Gonadoblastoma risk (Y+ patients)Prophylactic gonadectomy
FertilityAssisted reproduction (donor oocytes) in select mosaic patients; VTE risk with exogenous hormones
— Robbins & Kumar Basic Pathology; Robbins, Cotran & Kumar; Berek & Novak's Gynecology; Campbell-Walsh-Wein Urology
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