A 3-month-old boy born to a 38-year-old mother is brought to the pediatric clinic for developmental assessment. On examination, he has a broad flat face, upslanting palpebral fissures, a single palmar crease, and low-set ears. Cardiac auscultation reveals a systolic murmur. Developmental milestones are delayed. Karyotype analysis shows 47,XY,+21. Which of the following cardiac lesions is MOST commonly associated with this condition?

Explanation

## Diagnosis: Down Syndrome (Trisomy 21) **Key Point:** Down syndrome (trisomy 21) is the most common autosomal aneuploidy compatible with life, occurring in approximately 1 in 700 live births. The karyotype 47,XY,+21 confirms three copies of chromosome 21. ### Cardiac Manifestations in Down Syndrome | Cardiac Lesion | Frequency | Notes | |---|---|---| | **Endocardial cushion defect (AV canal)** | **40–50%** | **Most common; includes ASD, VSD, cleft mitral valve** | | Ventricular septal defect | 30–35% | Often part of AV canal defect | | Atrial septal defect | 10–15% | May occur alone or with other lesions | | Tetralogy of Fallot | 8–10% | Less common than AV canal | | Patent ductus arteriosus | 5–7% | Rare in Down syndrome | | Coarctation of aorta | <2% | Very rare | **High-Yield:** Endocardial cushion defects (atrioventricular canal defects) account for 40–50% of all congenital heart disease in Down syndrome, compared to only 2–3% in the general population. This is a pathognomonic association. ### Clinical Features of Down Syndrome **Craniofacial:** - Broad, flat face - Upslanting palpebral fissures - Epicanthal folds - Low-set ears - Protruding tongue **Extremities:** - Single palmar crease (simian crease) - Sandal gap (wide space between 1st and 2nd toe) - Hypotonia **Developmental:** - Intellectual disability (IQ 35–55 in moderate cases) - Delayed motor milestones - Speech delay **Systemic:** - Congenital heart disease (50–60%) - Gastrointestinal anomalies (duodenal atresia, Hirschsprung disease) - Refractive errors and hearing loss - Increased risk of leukemia (10–20× higher) - Thyroid dysfunction - Early-onset Alzheimer disease (by age 40–50) **Clinical Pearl:** The systolic murmur in this infant is most likely due to the left-to-right shunt across the endocardial cushion defect. Echocardiography is the gold standard for confirmation. **Mnemonic: CARDIAC features of Down Syndrome** - **C**ongenital heart disease (50–60%) - **A**trioventricular canal defect (most common) - **R**efractive errors and hearing loss - **D**uodenal atresia, GI anomalies - **I**ntellectual disability - **A**lzheimer disease (early onset) - **C**ancer risk (leukemia) ## Diagnostic Confirmation 1. **Karyotype:** Gold standard; shows 47 chromosomes with three copies of chromosome 21 2. **FISH (Fluorescence In Situ Hybridization):** Rapid confirmation 3. **Microarray:** Detects unbalanced rearrangements 4. **Prenatal screening:** Maternal serum markers (AFP, hCG, uE3) + nuchal translucency ultrasound ## Management - Cardiac evaluation: Echocardiography in all infants with Down syndrome - Early intervention: Physical therapy, occupational therapy, speech therapy - Screening: Vision, hearing, thyroid function, celiac disease - Surgical repair of cardiac defects if indicated - Regular monitoring for complications (leukemia, Alzheimer disease) [cite:Nelson Textbook of Pediatrics 21e Ch 77]