**Core Concept**
Tuberous sclerosis complex (TSC) is a genetic disorder characterized by the growth of non-cancerous tumors in various parts of the body, including the skin, brain, kidneys, and other organs. The condition is caused by mutations in either the TSC1 or TSC2 gene, leading to the activation of the mechanistic target of rapamycin (mTOR) pathway.

**Why the Correct Answer is Right**
The most common early finding in TSC is ash-leaf spots, which are hypopigmented macules that appear as a result of the loss of melanocytes. These spots are caused by the abnormal growth of neurons in the cerebral cortex, which leads to the formation of tubers. The mTOR pathway is hyperactivated in TSC, leading to the excessive growth of cells and the formation of tumors. Ash-leaf spots are often the first sign of TSC in infants and young children.

**Why Each Wrong Option is Incorrect**
**Option A:** Subependymal giant cell astrocytoma (SEGA) is a type of tumor that can occur in the brain in TSC patients, but it is not the most common early finding.
**Option B:** Renal angiomyolipomas are benign tumors that can occur in the kidneys in TSC patients, but they are not typically the first sign of the condition.
**Option C:** Cortical tubers are a hallmark of TSC, but they are not the most common early finding in patients with the condition.

**Clinical Pearl / High-Yield Fact**
Ash-leaf spots are a key diagnostic feature of TSC, and they can be seen in up to 90% of patients with the condition. They are often the first sign of TSC in infants and young children, and they can be used as a diagnostic criterion for the condition.

**Correct Answer: A. Ash-leaf spots.**