Which of the following post-birth factors is a toxin-related cause of intellectual disability?

• A. Lack of oxygen
• B. Cerebrovascular accidents
• C. Meningitis
• D. Lead and mercury poisoning

Answer: (D)

Toxin exposure after birth can injure the developing brain and lead to intellectual disability. Lead and mercury poisoning are classic examples of this. When these metals accumulate in a child’s brain, they disrupt key processes like neuron growth, synapse formation, and signaling, which can result in lower IQ, attention problems, and learning difficulties. Children are especially vulnerable because their bodies absorb more relative to their size and the brain is still maturing. In contrast, lack of oxygen causes brain injury through hypoxia, cerebrovascular accidents are strokes that damage brain tissue, and meningitis is an infection that inflames the brain—these are not toxin-related exposures.