**Core Concept**
Hirschsprung disease, also known as congenital aganglionic megacolon, is a condition that affects the large intestine (colon) and causes problems with passing stool. The underlying issue is related to the **enteric nervous system**, which controls the muscle contractions that move food, fluid, and air through the intestines. This condition is characterized by the absence of **ganglion cells** in the distal colon and rectum.

**Why the Correct Answer is Right**
The correct answer is related to the absence of **ganglion cells** in the **myenteric** and **submucosal** plexuses of the colon, which are crucial for the relaxation of the internal anal sphincter and the contraction of the muscularis mucosae. This absence leads to a functional obstruction because the affected segment of the colon cannot relax and pass stool, resulting in a buildup of stool behind the affected area.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because Hirschsprung disease is not primarily caused by a problem with the **muscularis mucosae** itself, but rather the lack of innervation.
**Option B:** Incorrect as it is not directly related to the primary cause of Hirschsprung disease.
**Option C:** Incorrect because, although **neurotransmitters** play a role in the enteric nervous system, their absence or malfunction is a consequence, not the primary cause.
**Option D:** Incorrect as the primary issue is not with the **colon** itself but with the nervous system controlling it.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that Hirschsprung disease typically presents in newborns with failure to pass meconium within the first 48 hours of life, followed by abdominal distension and vomiting.

**Correct Answer:** D. Absence of ganglion cells