Commonest cause of intestinal obstruction in down’s syndrome – a) Colomic atresia b) Intestinal atresiac) Duodenal atresia d) Oesophageal atresia

**Core Concept**
Intestinal obstruction in Down's syndrome is often associated with congenital anomalies of the gastrointestinal tract. The most common cause is a condition that affects the development of the small intestine.

**Why the Correct Answer is Right**
Duodenal atresia is a congenital anomaly characterized by the complete or partial absence of a segment of the duodenum, leading to intestinal obstruction. In Down's syndrome, duodenal atresia is the most common cause of intestinal obstruction, accounting for approximately 20-30% of cases. This is due to the abnormal development of the duodenum during embryogenesis, which is often disrupted in individuals with Down's syndrome.

**Why Each Wrong Option is Incorrect**
* **Option A:** Colonic atresia is a rare congenital anomaly that affects the large intestine, and it is not the most common cause of intestinal obstruction in Down's syndrome.
* **Option B:** Intestinal atresia refers to a general term that encompasses various types of atresias throughout the small intestine. While it is a possible cause of intestinal obstruction, it is not the most common cause in Down's syndrome.
* **Option D:** Oesophageal atresia is a congenital anomaly that affects the development of the esophagus, leading to feeding difficulties and respiratory problems. It is not typically associated with intestinal obstruction in Down's syndrome.

**Clinical Pearl / High-Yield Fact**
In individuals with Down's syndrome, duodenal atresia is often associated with other congenital anomalies, such as cardiac defects and gastrointestinal abnormalities. A high index of suspicion for duodenal atresia should be maintained in patients with Down's syndrome who present with symptoms of intestinal obstruction.

**Correct Answer: C. Duodenal atresia**