A 3-year-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. He has moderate intellectual disability and delayed speech. Cardiac auscultation reveals a systolic murmur. Karyotype analysis shows 47,XY,+21. Which of the following cardiac lesions is most commonly associated with this chromosomal abnormality?

Explanation

## Cardiac Manifestations in Down Syndrome (Trisomy 21) ### Chromosomal Basis **Key Point:** Down syndrome (trisomy 21) results from nondisjunction of chromosome 21, leading to three copies instead of two. This is the most common autosomal trisomy compatible with life. ### Cardiac Defects in Down Syndrome | Cardiac Lesion | Frequency in Down Syndrome | Frequency in General Population | Clinical Significance | |---|---|---|---| | **Endocardial cushion defect (AV canal)** | 40–50% | <1% | **Most common** — includes ostium primum ASD, cleft mitral valve, VSD | | Tetralogy of Fallot | 10–15% | 7–10% | More common than in general population but less than ECD | | Patent ductus arteriosus | 10% | 0.5–1% | Increased risk | | Ventricular septal defect | 30% | 2–3% | Often part of AV canal defect | | Atrial septal defect | 8–10% | 0.1% | Usually ostium secundum | | Transposition of great arteries | Rare | 3–5% | Not typically associated | | Coarctation of aorta | Rare | 0.4% | Not typically associated | **High-Yield:** Endocardial cushion defect (AV canal defect) is present in **40–50% of children with Down syndrome**, making it the single most common cardiac lesion. This is 40–50 times more frequent than in the general population. ### Clinical Pearl **Clinical Pearl:** The systolic murmur in this child is likely from a VSD component of the AV canal defect or from mitral regurgitation due to cleft mitral valve. Early echocardiographic screening is essential in all infants with Down syndrome. ### Pathophysiology Endocardial cushion defects arise from abnormal development of the endocardial cushions, which normally fuse to form the lower atrial septum, upper ventricular septum, and mitral and tricuspid valve leaflets. In Down syndrome, this developmental process is disrupted, leading to a spectrum of defects ranging from isolated ostium primum ASD to complete AV canal defect with common AV valve. ### Diagnostic Approach 1. **Clinical suspicion:** Systolic murmur + Down syndrome features 2. **Echocardiography:** Gold standard for diagnosis; shows ASD, VSD, and valve abnormalities 3. **Chest X-ray:** May show cardiomegaly and pulmonary congestion if heart failure present 4. **ECG:** Left axis deviation (unusual in children) is a clue to AV canal defect **Key Point:** Left axis deviation on ECG is a characteristic finding in AV canal defect and should raise suspicion even before echocardiography. ### Management - **Medical:** Diuretics and ACE inhibitors if heart failure develops - **Surgical:** Repair of AV canal defect is indicated if significant left-to-right shunt or valve regurgitation; timing depends on hemodynamic severity - **Endocarditis prophylaxis:** Indicated pre- and post-operatively ### Mnemonic for Down Syndrome Cardiac Defects **CAVEAT:** **C**ushion defects (endocardial), **A**trial septal defect, **V**entricular septal defect, **E**arly screening (echo), **A**V valve cleft, **T**etralogy (less common than ECD) **High-Yield:** Remember that while tetralogy of Fallot is common in the general population, in Down syndrome the **endocardial cushion defect is far more common** — this is a classic NEET PG discriminator question.