A child is brought to you with history of mental retardation. On examination you find that he also has dolichocephaly, low set ears, micrognathia, clenched hands with overlapping fingers, simian crease and rocker bottom feet. Which is the commonest cardiac lesion you would expect to find in this patient?

**Core Concept**
The patient described exhibits a combination of physical anomalies characteristic of Down syndrome, a genetic disorder caused by an extra copy of chromosome 21 (trisomy 21). This condition is associated with various congenital malformations and increased risk of certain medical complications.

**Why the Correct Answer is Right**
Children with Down syndrome are at a higher risk of developing cardiac anomalies, particularly atrioventricular septal defects (AVSD). AVSD is a congenital heart defect where there is a hole in the wall between the atria (upper chambers of the heart) and/or the ventricles (lower chambers of the heart). This defect can lead to abnormal blood flow between the atria and ventricles, potentially causing heart failure or other complications. The increased risk of AVSD in Down syndrome patients is thought to be related to the genetic alterations caused by the extra copy of chromosome 21.

**Why Each Wrong Option is Incorrect**
**Option A:** Ventricular septal defect (VSD) is a common congenital heart defect, but it is not the most common cardiac lesion associated with Down syndrome.
**Option B:** Tetralogy of Fallot (TOF) is a cyanotic congenital heart defect, but it is not specifically linked to Down syndrome.
**Option C:** Patent ductus arteriosus (PDA) is a common congenital heart defect, but it is not the most common cardiac lesion associated with Down syndrome.

**Clinical Pearl / High-Yield Fact**
Down syndrome patients are at increased risk of various cardiac anomalies, and a thorough cardiac evaluation is essential in the initial assessment of these patients.

**Correct Answer: C. Atrioventricular septal defect (AVSD).**

✓ Correct Answer: B. VSD