In a 24-year-old man with trisomy 21 (Down syndrome), which of the following statements is incorrect?

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E) Prenatal diagnosis via analysis of circulating fetal DNA is not possible - THIS IS THE INCORRECT STATEMENT

Prenatal diagnosis of trisomy 21 (Down syndrome) via cell-free DNA (cfDNA) analysis is absolutely possible and is now the most accurate screening test available. 1

Why Option E is Incorrect

Cell-free DNA screening (also called noninvasive prenatal testing/NIPS) has been validated and widely adopted for prenatal detection of trisomy 21:

  • Detection rate for trisomy 21: 99% with a screen positive rate of only 1-9%, far superior to traditional screening methods 1
  • cfDNA testing analyzes placental-derived DNA fragments (approximately 10-15% of total cfDNA in maternal plasma after 10 weeks gestation) using next-generation sequencing 1
  • The 2015 SMFM/ACOG guidelines specifically recommend cfDNA screening for women at increased risk of fetal aneuploidy, including those with ultrasound findings suggesting trisomy 21 1
  • More recent 2025 ACMG guidelines strongly recommend prenatal cfDNA screening for the general population over traditional methods for trisomies 21,18, and 13 2

Important caveat: While cfDNA is highly accurate screening, positive results require diagnostic confirmation via amniocentesis or chorionic villus sampling, as false positives can occur due to confined placental mosaicism, maternal mosaicism, or other factors 3

Why the Other Options Are Correct

A) Early-onset Alzheimer's dementia - CORRECT statement

  • Universal occurrence of Alzheimer disease histopathology with high prevalence of dementia in individuals with Down syndrome 4
  • This provides insights into Alzheimer disease pathology and treatment

B) Increased risk of leukemia - CORRECT statement

  • Well-established hematological complication in Down syndrome 4, 5

C) Average life expectancy of 55 years - CORRECT statement

  • Advances in medical care have led to longer lifespan and better quality of life 5
  • This represents significant improvement from historical data

D) Duodenal atresia and structural heart defects - CORRECT statement

  • Congenital heart diseases are highly prevalent (atrioventricular septal defect, atrial septal defect, patent ductus arteriosus, tetralogy of Fallot) 6, 4
  • Gastrointestinal anomalies including duodenal atresia are well-documented 4, 5

References

1
Guideline

#36: prenatal aneuploidy screening using cell-free dna.

American Journal of Obstetrics and Gynecology, 2015

4
Research

Down syndrome.

Nature reviews. Disease primers, 2020

5
Research

Advances in Down Syndrome.

Advances in pediatrics, 2026

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