**Core Concept**
Down's syndrome, a genetic disorder caused by an extra copy of chromosome 21, is associated with various medical complications. Individuals with Down's syndrome are at increased risk for certain health issues due to the genetic alterations.

**Why the Correct Answer is Right**
Down's syndrome is associated with an increased risk of congenital heart disease, particularly atrioventricular septal defects and ventricular septal defects. This is due to the altered expression of genes involved in cardiac development, such as **TBX5** and **GATA4**. The presence of congenital heart disease in Down's syndrome patients can lead to increased morbidity and mortality.

**Why Each Wrong Option is Incorrect**
* **Option A:** While Down's syndrome is indeed associated with an increased risk of congenital heart disease, other options are not as strongly linked to the condition. For example, **Option B** is incorrect as Acute Lymphoblastic Leukemia (ALL) is more commonly associated with Down's syndrome, but it's not the most correct association here.
* **Option B:** ALL is indeed associated with Down's syndrome, but it's not as strongly linked as congenital heart disease. The risk of ALL is increased due to the genetic alterations in Down's syndrome, particularly the **TCR** gene.
* **Option C:** Early onset Alzheimer's disease is associated with Down's syndrome, but it's not the most correct association in this context. Individuals with Down's syndrome are at increased risk of developing Alzheimer's disease, particularly after the age of 40.
* **Option D:** CNS tumors are not as strongly linked to Down's syndrome as congenital heart disease or ALL. While there may be an increased risk of certain CNS tumors, it's not as well-established as the other options.
* **Option E:** Infection is not a direct consequence of Down's syndrome, although individuals with the condition may be at increased risk of certain infections due to immunological abnormalities.

**Clinical Pearl / High-Yield Fact**
Individuals with Down's syndrome are at increased risk of various medical complications, including congenital heart disease, ALL, and Alzheimer's disease. It's essential to perform regular health screenings and provide appropriate medical care to manage these conditions.

**Correct Answer: A. Congenital heart disease**