**Core Concept**
Dubin-Johnson syndrome is a rare genetic disorder characterized by an inability to secrete conjugated bilirubin into the bile, resulting in a buildup of bilirubin in the blood. This condition is associated with a mutation in the **ABCC2** gene, which codes for a protein involved in the transport of bilirubin glucuronides. The **ABCC2** gene plays a crucial role in the liver's ability to transport and eliminate bilirubin.

**Why the Correct Answer is Right**
The correct answer is related to the **ABCC2** gene, as mutations in this gene have been identified as the primary cause of Dubin-Johnson syndrome. The **ABCC2** protein is a member of the ATP-binding cassette (ABC) transporter family and is responsible for the canalicular transport of bilirubin glucuronides. A defect in this gene leads to the accumulation of conjugated bilirubin in the liver, resulting in the characteristic symptoms of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not correspond to the known genetic defect associated with Dubin-Johnson syndrome.
**Option B:** This option is also incorrect as it is not related to the **ABCC2** gene or the transport of bilirubin glucuronides.
**Option C:** This option is incorrect because it is not associated with the genetic defect underlying Dubin-Johnson syndrome.

**Clinical Pearl / High-Yield Fact**
Dubin-Johnson syndrome is a rare but important condition to recognize, as it can be differentiated from other causes of jaundice by its characteristic liver discoloration and the presence of conjugated bilirubin in the blood. The diagnosis can be confirmed by genetic testing for mutations in the **ABCC2** gene.

**Correct Answer:** D. ABCC2 gene mutation