Okay, let's tackle this question. The patient is a 4-year-old boy with seizures, hypopigmented patches on the face, and mental retardation. The key here is to connect these symptoms to a specific condition.

First, I need to recall what conditions present with hypopigmented patches. Tuberous Sclerosis comes to mind because one of its hallmark signs is hypomelanotic macules, which are those light patches. Tuberous Sclerosis is a genetic disorder that causes benign tumors in various organs, including the brain, which can lead to seizures. The mental retardation is also a common feature because the brain abnormalities can affect cognitive development.

Now, the other options might be things like Neurofibromatosis, but that usually presents with café-au-lait spots, not hypopigmented ones. Incontinentia Pigmenti is another possibility, but that has a characteristic pattern of skin lesions that evolve over time, not hypopigmented patches. Sturge-Weber syndrome involves port-wine stains and neurological issues, but again, not hypopigmented patches.

So, the combination of hypopigmented patches, seizures, and mental retardation points most strongly to Tuberous Sclerosis. The clinical pearl here is to remember the "Three Hs" of Tuberous Sclerosis: Hypopigmented macules, Hamartomas, and Hydrocephalus, along with seizures and cognitive issues. The hypopigmented patches are often called ash-leaf spots and can be best seen under a Wood's lamp.

**Core Concept**
This question tests recognition of **tuberous sclerosis complex (TSC)**, a neurocutaneous syndrome characterized by seizures, intellectual disability, and hypopigmented skin lesions. Key features include **hamartomas** in the brain, skin, and other organs, with **hypomelanotic macules** (ash-leaf spots) as a diagnostic criterion.

**Why the Correct Answer is Right**
TSC is an autosomal dominant disorder caused by mutations in **TSC1** (hamartin) or **TSC2** (tuberin) genes, leading to dysregulated mTOR signaling and abnormal cell growth. The hypopigmented facial patches (ash-leaf spots), seizures (due to cortical tubers), and intellectual disability are classic triad features. Skin findings are often best visualized under **Wood’s lamp**.

**Why Each Wrong Option is Incorrect**
**Option A: Neurofibromatosis type 1** – Presents with **café-au-lait spots** and neurofibromas, not hypopigmented patches.
**Option B: Incontinentia pigmenti** – Features **swirling hyperpigmented/depigmented bands** in a "caterpillar" pattern, typically with systemic involvement in infants.
**Option C: Sturge-Weber syndrome** – Characterized by **port-wine stains** and leptomeningeal angiomatosis, not hypopigmentation.

**Clinical Pearl / High-Yield Fact**
Remember the **"Three Hs" of Tuberous Sclerosis**: **Hypopigmented macules**, **Hamartomas**, and **Hydrocephalus**, along with seizures and cognitive impairment. Ash-leaf spots are pathognomonic and often diagnostic when combined with other major criteria.

✓ Correct Answer: B. Tuberous sclerosis