Chromosomal Disorders & SyndromesMarch 21, 20262 min read

5-second rule for Turner syndrome

Quick-hit shareable content for Turner syndrome. Include visual/mnemonic device + one-liner explanation. System: Genetics.

5-second rule for Turner syndrome (Genetics)

If you have 5 seconds on an exam stem, think:

“Short girl + streak ovaries + no Barr body = Turner (45,X).”

The 5-Second Rule (One-Liner)

Turner syndrome is monosomy X (45,X) causing short stature and ovarian failure (streak ovaries) with classic neck/chest findings and left-sided heart defects.

Visual / Mnemonic Device: “XO = eXcluded Ovary”

Picture an X with the O missing → the ovary is “missing,” so you get streak ovaries and infertility.

XO →

  • X chromosome present, O missing → 45,X
  • Ovary failure → no estrogen → ↑ FSH/LH (hypergonadotropic hypogonadism)

High-Yield Snapshot (What USMLE wants you to recognize)

Core genetics

  • Karyotype: 45,X (monosomy X)
  • Barr body: Absent
    • (Rule: Barr bodies = # of X chromosomes − 1 → 1 X gives 0 Barr bodies)
  • Often due to meiotic nondisjunction or mosaicism (45,X/46,XX)
    • Mosaic cases may have milder features and sometimes some pubertal development.

5 Classic Clues in a Stem (Rapid pattern recognition)

  1. Short stature
  2. Webbed neck + low posterior hairline
  3. Shield chest with widely spaced nipples
  4. Primary amenorrhea / delayed puberty
  5. Congenital heart disease (especially left-sided)

Must-Know Associations (Step 1/2 Favorites)

Cardiac (very high-yield)

  • Coarctation of the aorta
  • Bicuspid aortic valve
  • Watch for: HTN, differential arm/leg BP, rib notching (coarctation)

Renal

  • Horseshoe kidney
  • Increased risk of UTIs and hydronephrosis

Reproductive / endocrine

  • Streak ovaries → ↓ estrogen → ↑ FSH, ↑ LH
  • Infertility (but pregnancy may be possible in some mosaic cases or with assisted reproduction)
  • Increased risk of hypothyroidism (often autoimmune)

Other common findings

  • Lymphedema of hands/feet in infancy
  • Hearing loss (recurrent otitis media)

Labs & Physiology in 10 Seconds

Turner = primary ovarian failure → ovaries can’t respond → pituitary compensates:

  • ↓ Estrogen
  • ↑ FSH and ↑ LH (hypergonadotropic hypogonadism)

Quick Differential: Don’t Confuse These

  • Turner (45,X): phenotypic female, short, streak ovaries, no Barr body, coarctation
  • Androgen insensitivity (46,XY): phenotypic female, normal/tall, undescended testes, sparse/absent pubic hair, no uterus
  • Klinefelter (47,XXY): phenotypic male, tall, small firm testes, infertility, 1 Barr body

One-Phrase Exam Stem Translation

If the question says:

  • “Teen girl, short stature, primary amenorrhea, webbed neck”
    → Turner syndrome (45,X) until proven otherwise.
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