**Core Concept**
The child's presentation suggests a neurocutaneous syndrome, where a skin manifestation (hypopigmented macules) is associated with neurological abnormalities (seizures and mental retardation). This condition involves a genetic disorder affecting both skin and brain development.

**Why the Correct Answer is Right**
The likely diagnosis is Tuberous Sclerosis Complex (TSC), a genetic disorder characterized by the growth of non-cancerous tumors in various parts of the body, including the skin, brain, and kidneys. The hypopigmented macules are a classic skin manifestation of TSC, known as ash-leaf spots. These spots are caused by the loss of melanocytes in the skin, resulting from mutations in the TSC1 or TSC2 genes. The seizures and mental retardation are due to the development of cortical tubers in the brain, which disrupt normal brain function.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the child's presentation. Neurofibromatosis type 1 (NF1) typically presents with café-au-lait macules, not hypopigmented macules.
**Option B:** This option is incorrect because it is not a known neurocutaneous syndrome. The child's presentation does not match the typical features of Sturge-Weber syndrome, which involves a port-wine stain and leptomeningeal angiomatosis.
**Option C:** This option is incorrect because it is not a specific diagnosis. The child's presentation is too specific to be attributed to a general category like "neurological disorder."

**Clinical Pearl / High-Yield Fact**
Remember that TSC is a genetic disorder with variable expression, and the presence of hypopigmented macules (ash-leaf spots) is a key diagnostic clue. These spots can be present at birth or appear in early childhood.

**Correct Answer:** C.