The Seychelles child development study: Results and new directions through twenty-nine months

The Seychelles Child Development Study was begun in 1986 to prospectively examine the association between child development and prenatal and postnatal methylmercury exposure from a high fish diet. Hair mercury levels from mothers and children are used as the index of exposure. A cross- sectional Pilot Study of 789 infants suggested that prenatal mercury exposure may affect development and that the effect decreased with age independently of exposure. A follow up of 217 Pilot Study children at 66 months of age also suggested that neurodevelopmental effects of prenatal exposure might be present, but the associations were dependent on outcomes in a small number of children. On the basis of the initial results of the Pilot Study a prospective, longitudinal Main Study, with more data on confounding variables and more extensive developmental testing, was begun on a new cohort of 779 children. No association between prenatal exposure and primary neurodevelopmental outcomes was seen at 6 1/2, 19, or 29 months of age. There was an inverse relationship at 29 months in boys only between maternal hair mercury level and activity level, as judged by the examiner during the testing session (one of seven behavioral subscales of the Infant Behavior Record, of the Bayley Scales of Infant Development). In addition to an interaction between maternal hair level and gender, subsequent, secondary analyses are examining interactions between mercury level and a number of socioeconomic factors. Secondary analyses of developmental milestones, similar to those used in the Iraq study, are also under way. Although the association with activity suggests the need for further study of this cohort, no definite adverse neurodevelopmental effects from fetal mercury exposure have been detected through 29 months of age. In a related study, brains were obtained at autopsy from thirty-two Seychellois infants. Tissue from six different brain regions was examined histologically and analyzed for mercury. No definite histological abnormalities were found. Mercury levels ranged from about 50 ppb to 300 ppb and there was good correlation among brain regions. For 27 brains maternal hair from delivery was available and maternal hair mercury levels correlated well with levels in infant brain.