Human brain disturbance by methylmercury poisoning, focusing on the long-term effect on brain weight.

The long-term effects of the initial methylmercury exposure in the Minamata area were examined, with focus on brain weight. Comparisons were made between the brain weights of methylmercury-contaminated persons in the Minamata area (cases) and those of Japanese who suffered sudden or accidental death without brain disease (controls). Since over thirty years have passed since the outbreak of Minamata disease, subjects aged 30 or over at death were included in the analysis. The total number of cases was 417 (273 males, 144 females) and that of controls was 2,934 (2,174 males, 760 females). The data suggest that the brain weights from Minamata cases were reduced by 80 to 200g as compared to the controls. These results may indicate that methylmercury exposure led to a decrease of nerve cells (single cell necrosis), so-called "thinning out", in the brain cortex.