**Core Concept:** Tuberous Sclerosis Complex (TSC) is a genetic disorder characterized by the formation of benign tumors in various organs, particularly the brain, kidneys, and lungs. It is caused by mutations in either the TSC1 or TSC2 gene, leading to impaired function of the tuberous sclerosis complex (TSC) protein. The TSC protein inhibits the mammalian target of rapamycin (mTOR) pathway, a key regulator of cell growth and proliferation.

**Why the Correct Answer is Right:** The correct answer is "D. Hypopigmentation" because TSC does not cause hypopigmentation, which is a reduction in skin pigmentation. In contrast, TSC is associated with increased pigmentation due to the formation of benign tumors (hamartomas) in various organs, including skin lesions like angiofibromas, shagreen patches, and café-au-lait spots.

**Why Each Wrong Option is Incorrect:**

A. **Hypotonia (low muscle tone):** While TSC can cause muscle hypotonia in infants, it is not a specific feature of the condition. Hypotonia is also seen in other conditions like neuromuscular disorders, and excluding the other options helps identify TSC.

B. **Hypopigmentation:** As mentioned earlier, TSC leads to increased pigmentation, not hypopigmentation.

C. **Hypothyroidism:** Although TSC can be associated with thyroid abnormalities, hypothyroidism is not a typical feature and does not specifically contradict the correct answer.

**Clinical Pearl:** Tuberous Sclerosis Complex can present with various clinical features, including seizures, developmental delays, and renal angiomyolipoma. Identifying the absence of hypopigmentation, hypotonia, and hypothyroidism can help differentiate TSC from other conditions sharing similar symptoms. Regular monitoring and management of seizures, kidney function, and mental development are essential for affected individuals.