**Core Concept**
Tuberous sclerosis 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 disorder is caused by mutations in the TSC1 or TSC2 genes, leading to abnormal cell growth and tumor formation.

**Why the Correct Answer is Right**
The earliest feature of tuberous sclerosis is often a skin lesion known as an **adenoma sebaceum**. These lesions are typically facial angiofibromas that appear in early childhood, usually between 3-6 months of age. They are caused by the abnormal growth of fibrous connective tissue and are a hallmark of the disorder. The mechanism behind adenoma sebaceum involves the activation of the mammalian target of rapamycin (mTOR) pathway, which is a key regulator of cell growth and proliferation.

**Why Each Wrong Option is Incorrect**
**Option A:** **Ash-Leaf spots** are indeed a feature of tuberous sclerosis, but they are not the earliest feature. Ash-leaf spots are hypopigmented macules that appear in the first few months of life.
**Option B:** **Subependymal nodules** are a type of brain lesion found in tuberous sclerosis, but they are not the earliest feature of the disorder.
**Option C:** **Renal angiomyolipomas** are benign tumors of the kidney that can occur in tuberous sclerosis, but they are not typically the first manifestation of the disorder.

**Clinical Pearl / High-Yield Fact**
Tuberous sclerosis is a multisystem disorder that can affect multiple organ systems, including the skin, brain, kidneys, and heart. It is essential to be aware of the various features of the disorder, including adenoma sebaceum, ash-leaf spots, subependymal nodules, and renal angiomyolipomas, to make an accurate diagnosis.

**Correct Answer:** A. Adenoma sebaceum.