**Core Concept**
Irritable bowel syndrome (IBS) is a **functional gastrointestinal disorder** characterized by recurrent abdominal pain associated with changes in bowel habits, such as **diarrhea** or **constipation**. The exact pathophysiology of IBS is unclear, but it involves a combination of **motility disorders**, **visceral hypersensitivity**, and **psychological factors**.

**Why the Correct Answer is Right**
The correct answer is related to the **pathophysiology** and **clinical presentation** of IBS. IBS is often associated with **stress** and **anxiety**, which can exacerbate symptoms. The **brain-gut axis** plays a crucial role in the development and maintenance of IBS symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because IBS is not typically associated with **inflammatory changes**.
**Option B:** This option is incorrect because IBS is not caused by a **single genetic mutation**.
**Option C:** This option is incorrect because IBS is not typically characterized by **structural abnormalities**.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that IBS is a **diagnosis of exclusion**, meaning that other potential causes of symptoms, such as **inflammatory bowel disease**, must be ruled out before making a diagnosis of IBS.

**Correct Answer:** D. IBS is a functional gastrointestinal disorder characterized by abdominal pain and changes in bowel habits.