Long-term neurological and neurocognitive deficits in adults prenatally exposed to methylmercury: Minamata disease.

Minamata disease, officially recognized in 1956, is a well-known food poisoning event that was caused by the consumption of fish and seafood contaminated with methylmercury. Although patients with congenital Minamata disease (CMD) with severe neurological impairments after birth are widely recognized, few studies have examined the effects of prenatal methylmercury exposure among residents, which is likely at lower levels than in CMD patients. We aimed to investigate the relationship between prenatal methylmercury exposure and subsequent neurological and neurocognitive outcomes. We conducted a cross-sectional study during 2024-2025 among 51 individuals aged approximately 70 years, 27 residents from an existing cohort established in 1970 in Minamata and 24 age-matched individuals who had lived in less-exposed regions. We performed a battery of neurological and neurocognitive tests in both groups and compared the results using multiple linear regression analyses. We also examined the association between intelligence scores obtained in 1970, and intelligence scores obtained in the present investigation, only among exposed participants. We found that exposed individuals had unfavorable neurological and neurocognitive test scores, in comparison with less-exposed controls. Scores on the Montreal Cognitive Assessment, Japanese Edition were 5.91 points lower (95% confidence interval: 3.09 to 8.73) for exposed residents than for the less-exposed group. Moreover, intelligence scores evaluated during exposed participants' adolescence were correlated with their neurocognitive scores in adulthood. Our findings showed that prenatal methylmercury exposure affected subsequent neurological and neurocognitive functions, including among individuals with lower exposure than in CMD patients, and even approximately 70 years after the initial exposure.