**Core Concept**
Acanthosis nigricans is a skin condition characterized by dark, velvety skin patches, typically found in the folds and creases of the body. This condition is associated with insulin resistance and is often seen in patients with type 2 diabetes mellitus. The pathophysiology involves increased insulin levels, which stimulate the growth of skin cells.

**Why the Correct Answer is Right**
The correct answer is related to insulin resistance, which is a key factor in the development of acanthosis nigricans. Insulin resistance leads to increased insulin levels, which in turn stimulate the growth of skin cells, resulting in the characteristic skin lesions. This is often seen in patients with type 2 diabetes mellitus, obesity, and polycystic ovary syndrome (PCOS).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while acanthosis nigricans can be associated with other conditions, it is not primarily caused by a genetic disorder.
**Option B:** This option is incorrect because while skin conditions like eczema and psoriasis can present with skin lesions, they are not directly related to insulin resistance.
**Option C:** This option is incorrect because while certain medications can cause skin reactions, they are not a primary cause of acanthosis nigricans.

**Clinical Pearl / High-Yield Fact**
Acanthosis nigricans is often seen in patients with insulin resistance, and it can be a useful clinical sign to identify patients at risk of developing type 2 diabetes mellitus.

**Correct Answer: D. Insulin resistance.**