Association between prenatal exposure to methylmercury and cognitive functioning in seychellois children: A reanalysis of the McCarthy Scales of Children's Ability from the main cohort study

Methylmercury (MeHg) is a neurotoxicant whose high-dose effects first becam e known following a number of poisoning outbreaks that occurred worldwide. The primary human exposure is low dosage from fish consumption. Studies of fish-eating populations have not found a consistent pattern of association between exposures and outcomes. Therefore, examining specific areas of cogn itive functioning has been suggested as an important approach to determine whether more subtle effects of MeHg exposure are present. In the Seychelles longitudinal study of prenatal and postnatal MeHg exposure from fish consu mption and development, the McCarthy Scales of Children's Abilities (MSCA) were administered to children at age 66 months. No association between MeHg exposure and performance on the MSCA General Cognitive Index was identifie d. We analyzed these data further to deter mine whether associations were p resent an specific subscales of the MSCA. The standard MSCA subscales were analyzed. Then, more specific subscales of the MSCA were defined and analyz ed utilizing a neuro psychological approach. The subscales were recombined to approximate the domains of cognitive functioning evaluated in the Faroes and New Zealand studies. Analyses of both the standard and the recombined MSCA subscales showed no adverse associations with MeHg exposure and neurop sychological endpoints. A positive association between postnatal MeHg expos ure and performance on the MSCA Memory subscale was found. These findings a re consistent with previous reports from the Seychelles study in that no ad verse effects of MeHg exposure from fish consumption can be detected in thi s cohort. (C) 2000 Academic Press.