Tohoku J. Exp. Med., 2017 May, 242(1)

Psychomotor Ability in Children Prenatally Exposed to Methylmercury: The 18-Month Follow-Up of Tohoku Study of Child Development

NOZOMI TATSUTA,^1,2 KATSUYUKI MURATA,² MIYUKI IWAI-SHIMADA,³ KOZUE YAGINUMA-SAKURAI,⁴ HIROSHI SATOH⁵ and KUNIHIKO NAKAI¹

¹Development and Environmental Medicine, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
²Department of Environmental Health Sciences, Akita University Graduate School of Medicine, Akita, Akita, Japan
³Centre for Health and Environmental Risk Research, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
⁴Department of Human Health and Nutrition, Shokei Gakuin University Faculty of Comprehensive Human Science, Natori, Miyagi, Japan
⁵Environmental Health Sciences, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan

Fish contain nutrients essential to the developing fetal brain, but they are contaminated with methylmercury. The Tohoku Study of Child Development, now underway in the Sanriku coastal area of Miyagi prefecture, Japan, follows mother-child pairs to examine the risks and benefits of fish consumption during pregnancy, especially the effects of prenatal exposures to methylmercury, selenium, and docosahexaenoic acid (DHA) on child neurodevelopment. Children aged 18 months were administered the Bayley Scales of Infant Development second edition (BSID-II) and Kyoto Scale of Psychological Development (KSPD) in 2004-2008. Complete data of cord-blood total mercury (THg), cord-plasma selenium, maternal-plasma DHA, the above test scores, and confounders for 566 mother-child pairs were available. The median cord-blood THg level was 15.7 (range, 2.7-96.1) ng/g. Since the BSID-II and KSPD scores were significantly lower in the 285 boys than in the 281 girls, analyses were conducted separately. The Psychomotor Development Index (PDI) of BSID-II was significantly correlated with cord-blood THg only in the boys, and significance of the association remained unchanged after adjusting for possible confounders; i.e., a 10-fold increase in cord-blood THg was associated with a 8.3-point decrease in the score of the PDI. Other significant correlations of THg were not seen in the boys or girls. Selenium and DHA showed no significant correlations with the BSID-II or KSPD scores in either sex. In conclusion, intrauterine methylmercury exposure may affect psychomotor development, and boys appear to be more vulnerable to the exposure than girls.

keywords —— docosahexaenoic acid; methylmercury; psychomotor development; selenium; sex difference

© 2017 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2017, 242, 1-8

Correspondence: Kunihiko Nakai, Ph.D., Development and Environmental Medicine, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan.

e-mail: nakaik@med.tohoku.ac.jp