The correct answer is Mercury.

- Minamata disease is a neurological syndrome caused by severe mercury poisoning.
- It was first identified in the 1950s in Minamata Bay, Japan, where industrial discharge of methylmercury contaminated the water supply, leading to the bioaccumulation of mercury in fish and shellfish.
- When consumed by local populations, this resulted in widespread mercury toxicity.

Key points:
- Mercury exposure—specifically in the form of organic mercury compounds like methylmercury—is responsible for Minamata disease.
- The disease primarily affects the central nervous system (CNS), causing severe neurological damage.
- Developing fetuses are especially vulnerable, often suffering from profound congenital disabilities, including cerebral palsy-like symptoms, mental retardation, and motor dysfunction.
- Other heavy metals, such as lead, arsenic, and cadmium, cause different clinical manifestations and are not associated with the syndrome seen in Minamata disease.

Thus, the hallmark feature of Minamata disease is CNS damage secondary to methylmercury exposure.

Reference: Goldfrank's Toxicologic Emergencies, 12th Edition, Chapter 58: Heavy Metal Toxicity