One-page cheat sheet: Edwards syndrome (Trisomy 18)

Edwards syndrome (Trisomy 18) is a chromosomal aneuploidy classically due to meiotic nondisjunction (usually maternal). On USMLE, it’s tested as a high-mortality trisomy with a distinct constellation of craniofacial, limb, cardiac, and renal findings.

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One-liner (USMLE-ready)

Trisomy 18 (Edwards) = severe developmental delay + congenital heart disease + clenched fists with overlapping fingers + rocker-bottom feet, with high infant mortality.

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The visual + mnemonic device (fast recall)

“18 = ‘EIGHTEEN’ has 8 letters → think: clenched fists”

Picture a baby gripping the number 18:

• Clenched fists
• Overlapping fingers (index over middle is a common depiction)
• Rocker-bottom feet “rocking” the 18

Mnemonic: Edwards = Eighteen = Everything clenched

• Ears low-set
• Extra (overlapping) fingers position
• Elevated mortality (early)

(Use whichever sub-mnemonic sticks—USMLE rewards pattern recognition.)

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Core diagnosis snapshot

• Karyotype: 47,XX,+18 or 47,XY,+18
• Mechanism: Nondisjunction (risk increases with advanced maternal age)
• Screening clue: Increased nuchal translucency on first-trimester ultrasound (nonspecific aneuploidy clue)
• Confirmatory testing: CVS or amniocentesis with fetal karyotype / chromosomal microarray
  • (On exams: definitive diagnosis requires fetal genetic testing.)

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Hallmark clinical features (high-yield)

Craniofacial

• Prominent occiput
• Low-set ears
• Micrognathia (small jaw)

Limbs

• Clenched hands with overlapping fingers (very classic)
• Rocker-bottom feet (convex sole)

Cardiac (common cause of morbidity)

• Congenital heart defects, especially:
  • VSD
  • ASD
  • PDA
    (USMLE often expects “CHD is common” even if a specific lesion isn’t named.)

Renal / other

• Renal anomalies (varied)
• Severe intellectual disability / growth restriction

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Prognosis (testable)

• High infant mortality: many infants die within the first year (often much earlier)
• Survivors have severe developmental impairment and complex medical needs

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How USMLE likes to ask it (patterns)

Look for a newborn with:

• IUGR, feeding/respiratory difficulty, CHD
• Prominent occiput + micrognathia
• Clenched fists with overlapping fingers
• Rocker-bottom feet

Then pick: Trisomy 18 (Edwards syndrome).

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Differentials: don’t mix these up

Trisomy 21 (Down)

• Upward slanting palpebral fissures, single palmar crease, duodenal atresia, endocardial cushion defects, ALL/AML (M7), Alzheimer risk

Trisomy 13 (Patau)

• Cleft lip/palate, holoprosencephaly, polydactyly, cutaneous scalp defects, omphalocele

Edwards (18) is the one with: clenched fists + overlapping fingers + rocker-bottom feet + prominent occiput.

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Quick table (rapid review)

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Rapid-fire “if you remember only 3 things”

1. Clenched hands + overlapping fingers = Edwards until proven otherwise.
2. Rocker-bottom feet + prominent occiput strongly supports Trisomy 18.
3. High infant mortality + CHD are core board-relevant associations.