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Turner syndrome md pathology exam question robbins based answer

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Turner Syndrome

Definition: Turner syndrome is a chromosomal disorder in phenotypic females caused by complete or partial monosomy of the X chromosome, resulting chiefly in gonadal dysgenesis and short stature.

Karyotype

  • 45,X: about 57% of cases.
  • Structural X-chromosome abnormalities: about 14%.
    • Isochromosome of the long arm: 46,X,i(Xq)
    • Ring X chromosome: 46,X,r(X)
    • Deletions: 46,X,del(Xp) or 46,X,del(Xq)
  • Mosaic forms: about 29%.
    • 45,X/46,XX
    • 45,X/46,XY
    • 45,X/47,XXX
Phenotype is variable, and is generally milder in mosaics or deletion variants.

Pathogenesis

  • Loss of one X chromosome causes haploinsufficiency of genes that normally escape X-inactivation.
  • Deletion of the SHOX gene at Xp22.33 causes short stature.
  • Ovarian development requires two active X chromosomes during oogenesis. Loss of X-chromosomal material leads to accelerated germ-cell loss and streak ovaries.
  • Other X-linked genes contribute to cardiovascular, renal, and endocrine abnormalities.

Morphology

  • Ovaries: transformed into bilateral, white streak gonads, composed of fibrous stroma and lacking follicles.
  • External genitalia are female but may remain infantile because of estrogen deficiency.
  • Congenital cardiovascular and renal malformations may be present.

Clinical Features

At birth / childhood
  • Short stature and growth retardation.
  • Lymphedema of hands and feet.
  • Nuchal edema due to distended lymphatics, later producing a webbed neck.
  • Low posterior hairline.
  • Shield chest with widely spaced nipples.
  • Cubitus valgus.
  • High-arched palate.
Associated malformations
  • Coarctation of aorta and bicuspid aortic valve.
  • Horseshoe kidney and other renal anomalies.
At puberty
  • Failure of normal sexual maturation.
  • Minimal breast development and scant pubic hair.
  • Primary amenorrhea and infertility due to ovarian failure.
Other associations
  • Intelligence is usually normal, though visual-spatial processing difficulties can occur.
  • Autoimmune hypothyroidism is common, particularly in those with an isochromosome X abnormality.
  • Cardiovascular disease is an important cause of childhood mortality.

Important exam point: Y chromosome material

About 5% to 10% of mosaic Turner cases contain Y-chromosome sequences, for example 45,X/46,XY. Such patients have increased risk of gonadoblastoma. Therefore, streak gonads are generally removed prophylactically when Y-chromosome material is identified.

Diagnosis

  • Clinical suspicion: short stature plus primary amenorrhea in a phenotypic female.
  • Confirm with karyotyping. FISH or chromosomal microarray may help identify mosaicism or occult Y-chromosome material.
  • Evaluate for cardiac, renal, thyroid, hearing, and metabolic abnormalities.

One-line answer

Turner syndrome is a phenotypic-female disorder caused by complete or partial monosomy X, classically 45,X, characterized by short stature, webbed neck, congenital cardiac and renal anomalies, streak ovaries causing hypergonadotropic hypogonadism, primary amenorrhea, and infertility.
Robbins & Kumar Basic Pathology, Turner Syndrome, p. 128-129.
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