Gary J. Myers

Prenatal methylmercury exposure from ocean fish consumption in the Seychelles child development study

INTRODUCTION Exposure to methylmercury (MeHg) before birth can adversely affect childrens neurodevelopment. The most common form of prenatal exposure is maternal fish consumption, but whether such exposure harms the fetus is unknown. We aimed to identify adverse neurodevelopmental effects in a fish-consuming population. METHODS We investigated 779 mother-infant pairs residing in the Republic of Seychelles. Mothers reported consuming fish on average 12 meals per week. Fish in Seychelles contain much the same concentrations of MeHg as commercial ocean fish elsewhere. Prenatal MeHg exposure was determined from maternal hair growing during pregnancy. We assessed neurocognitive, language, memory, motor, perceptual-motor, and behavioural functions in children at age 9 years. The association between prenatal MeHg exposure and the primary endpoints was investigated with multiple linear regression with adjustment for covariates that affect child development. FINDINGS Mean prenatal MeHg exposure was 6.9 parts per million (SD 4.5 ppm). Only two endpoints were associated with prenatal MeHg exposure. Increased exposure was associated with decreased performance in the grooved pegboard using the non-dominant hand in males and improved scores in the hyperactivity index of the Conners teacher rating scale. Covariates affecting child development were appropriately associated with endpoints. INTERPRETATION These data do not support the hypothesis that there is a neurodevelopmental risk from prenatal MeHg exposure resulting solely from ocean fish consumption.

Associations of maternal long-chain polyunsaturated fatty acids, methyl mercury, and infant development in the Seychelles Child Development Nutrition Study.

Fish consumption during gestation can provide the fetus with long-chain polyunsaturated fatty acids (LCPUFA) and other nutrients essential for growth and development of the brain. However, fish consumption also exposes the fetus to the neurotoxicant, methyl mercury (MeHg). We studied the association between these fetal exposures and early child development in the Seychelles Child Development Nutrition Study (SCDNS). Specifically, we examined a priori models of Omega-3 and Omega-6 LCPUFA measures in maternal serum to test the hypothesis that these LCPUFA families before or after adjusting for prenatal MeHg exposure would reveal associations with child development assessed by the BSID-II at ages 9 and 30 months. There were 229 children with complete outcome and covariate data available for analysis. At 9 months, the PDI was positively associated with total Omega-3 LCPUFA and negatively associated with the ratio of Omega-6/Omega-3 LCPUFA. These associations were stronger in models adjusted for prenatal MeHg exposure. Secondary models suggested that the MeHg effect at 9 months varied by the ratio of Omega-6/Omega-3 LCPUFA. There were no significant associations between LCPUFA measures and the PDI at 30 months. There were significant adverse associations, however, between prenatal MeHg and the 30-month PDI when the LCPUFA measures were included in the regression analysis. The BSID-II mental developmental index (MDI) was not associated with any exposure variable. These data support the potential importance to child development of prenatal availability of Omega-3 LCPUFA present in fish and of LCPUFA in the overall diet. Furthermore, they indicate that the beneficial effects of LCPUFA can obscure the determination of adverse effects of prenatal MeHg exposure in longitudinal observational studies.

Neurodevelopmental Effects of Maternal Nutritional Status and Exposure to Methylmercury from Eating Fish during Pregnancy

Fish contain nutrients that promote optimal brain growth and development but also contain methylmercury (MeHg) that can have toxic effects. The present study tested the hypothesis that the intake of selected nutrients in fish or measures of maternal nutritional status may represent important confounders when estimating the effects of prenatal methylmercury exposure on child development. The study took place in the Republic of Seychelles, an Indian Ocean archipelago where fish consumption is high. A longitudinal cohort study design was used. A total of 300 mothers were enrolled early in pregnancy. Nutrients considered to be important for brain development were measured during pregnancy along with prenatal MeHg exposure. The children were evaluated periodically to age 30 months. There were 229 children with complete outcome and covariate data for analysis. The primary endpoint was the Bayley Scales of Infant Development-II (BSID-II), administered at 9 and 30 months of age. Combinations of four secondary measures of infant cognition and memory were also given at 5, 9 and 25 months. Cohort mothers consumed an average of 537 g of fish (nine meals containing fish) per week. The average prenatal MeHg exposure was 5.9 ppm in maternal hair. The primary analysis examined the associations between MeHg, maternal nutritional measures and childrens scores on the BSID-II and showed an adverse association between MeHg and the mean Psychomotor Developmental Index (PDI) score at 30 months. Secondary analyses of the association between the PDI and only MeHg alone or nutritional factors alone showed only a borderline significant association between MeHg and the PDI at 30 months and no associations with nutritional factors. One experimental measure at 5 months of age was positively associated with iodine status, but not prenatal MeHg exposure. These findings suggest a possible confounding role of maternal nutrition in studies examining associations between prenatal MeHg exposures and developmental outcomes in children.

ACTH and prednisone in childhood seizure disorders

We treated 116 children with ACTH or prednisone. Fifty-two had infantile spasms with hypsarhythmia, and 64 had other types of intractable seizures. ACTH completely controlled seizures in all patients with infantile spasms and hypsarhythmia and 74% of those with other types of seizures. Prednisone controlled 51% of patients with infantile spasms and none with other seizures. Serious side effects were minimal for both drugs, and recurrent seizures occurred in 40 to 50% of patients within 4 to 14 months after completion of therapy.

Are Outcomes of Extremely Preterm Infants Improving? Impact of Bayley Assessment on Outcomes

OBJECTIVES To compare 18- to 22-month cognitive scores and neurodevelopmental impairment (NDI) in 2 time periods using the National Institute of Child Health and Human Developments Neonatal Research Network assessment of extremely low birth weight infants with the Bayley Scales of Infant Development, Second Edition (Bayley II) in 2006-2007 (period 1) and using the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley III), with separate cognitive and language scores, in 2008-2011 (period 2). STUDY DESIGN Scores were compared with bivariate analysis, and regression analyses were run to identify differences in NDI rates. RESULTS Mean Bayley III cognitive scores were 11 points higher than mean Bayley II cognitive scores. The NDI rate was reduced by 70% (from 43% in period 1 to 13% in period 2; P < .0001). Multivariate analyses revealed that Bayley III contributed to a decreased risk of NDI by 5 definitions: cognitive score <70 and <85, cognitive or language score <70; cognitive or motor score <70, and cognitive, language, or motor score <70 (P < .001). CONCLUSION Whether the Bayley III is overestimating cognitive performance or whether it is a more valid assessment of emerging cognitive skills than the Bayley II is uncertain. Because the Bayley III identifies significantly fewer children with disability, it is recommended that all extremely low birth weight infants be offered early intervention services at the time of discharge from the neonatal intensive care unit, and that Bayley scores be interpreted with caution.

Neurodevelopmental Outcomes in the Early CPAP and Pulse Oximetry Trial

BACKGROUND Previous results from our trial of early treatment with continuous positive airway pressure (CPAP) versus early surfactant treatment in infants showed no significant difference in the outcome of death or bronchopulmonary dysplasia. A lower (vs. higher) target range of oxygen saturation was associated with a lower rate of severe retinopathy but higher mortality. We now report longer-term results from our prespecified hypotheses. METHODS Using a 2-by-2 factorial design, we randomly assigned infants born between 24 weeks 0 days and 27 weeks 6 days of gestation to early CPAP with a limited ventilation strategy or early surfactant administration and to lower or higher target ranges of oxygen saturation (85 to 89% or 91 to 95%). The primary composite outcome for the longer-term analysis was death before assessment at 18 to 22 months or neurodevelopmental impairment at 18 to 22 months of corrected age. RESULTS The primary outcome was determined for 1234 of 1316 enrolled infants (93.8%); 990 of the 1058 surviving infants (93.6%) were evaluated at 18 to 22 months of corrected age. Death or neurodevelopmental impairment occurred in 27.9% of the infants in the CPAP group (173 of 621 infants), versus 29.9% of those in the surfactant group (183 of 613) (relative risk, 0.93; 95% confidence interval [CI], 0.78 to 1.10; P=0.38), and in 30.2% of the infants in the lower-oxygen-saturation group (185 of 612), versus 27.5% of those in the higher-oxygen-saturation group (171 of 622) (relative risk, 1.12; 95% CI, 0.94 to 1.32; P=0.21). Mortality was increased with the lower-oxygen-saturation target (22.1%, vs. 18.2% with the higher-oxygen-saturation target; relative risk, 1.25; 95% CI, 1.00 to 1.55; P=0.046). CONCLUSIONS We found no significant differences in the composite outcome of death or neurodevelopmental impairment among extremely premature infants randomly assigned to early CPAP or early surfactant administration and to a lower or higher target range of oxygen saturation. (Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the National Heart, Lung, and Blood Institute; SUPPORT ClinicalTrials.gov number, NCT00233324.).

Early clinical manifestations and intellectual outcome in children with symptomatic congenital cytomegalovirus infection

The Developmental Profile was completed on 32 prospectively followed children with symptomatic congenital cytomegalovirus infection (mean age 6 7/12 years; 78% white, 59% male). The distribution of intelligence and general developmental scores was bimodal; one group had severe deficits (mean IQ 28.8), the other had relatively less severe intellectual sequelae (mean IQ 91.6). Correlation analysis (Pearson r) showed that three variables--microcephaly, neurologic abnormalities, and chorioretinitis--when apparent during the first year of life, were all significantly associated with low intelligence. No correlation was found between IQ and severity of neonatal reticuloendothelial disease or hearing loss. Multiple regression analysis showed that age at testing, chorioretinitis, and neurologic sequelae accounted for 63% of the IQ variance in our sample. We conclude that children with symptomatic congenital cytomegalovirus infection have a greater range of intellectual outcomes than has been previously reported, and that certain early clinical manifestations may be useful in anticipating special needs.

Postnatal Exposure to Methyl Mercury from Fish Consumption: a Review and New Data from the Seychelles Child Development Study

BACKGROUND Fish is an important source of nutrition worldwide. Fish contain both the neurotoxin methyl mercury (MeHg) and nutrients important for brain development. The developing brain appears to be most sensitive to MeHg toxicity and mothers who consume fish during pregnancy expose their fetus prenatally. Although brain development is most dramatic during fetal life, it continues for years postnatally and additional exposure can occur when a mother breast feeds or the child consumes fish. This raises the possibility that MeHg might influence brain development after birth and thus adversely affect childrens developmental outcomes. We reviewed postnatal MeHg exposure and the associations that have been published to determine the issues associated with it and then carried out a series of analyses involving alternative metrics of postnatal MeHg exposure in the Seychelles Child Development Study (SCDS) Main Cohort. METHODS The SCDS is a prospective longitudinal evaluation of prenatal MeHg exposure from fish consumption. The Main Cohort includes 779 subjects on whom recent postnatal exposure data were collected at the 6-, 19-, 29-, 66-, and 107-month evaluations. We examined the association of recent postnatal MeHg exposure with multiple 66- and 107-month outcomes and then used three types of alternative postnatal exposure metrics to examine their association with the childrens intelligence quotient (IQ) at 107 months of age. RESULTS Recent postnatal exposure at 107 months of age was adversely associated with four endpoints, three in females only. One alternative postnatal metric was beneficially associated with 9-year IQ in males only. CONCLUSIONS We found several associations between postnatal MeHg biomarkers and childrens developmental endpoints. However, as has been the case with prenatal MeHg exposure in the SCDS Main Cohort study, no consistent pattern of associations emerged to support a causal relationship.

The Chemical Nature of Mercury in Human Brain Following Poisoning or Environmental Exposure

Methylmercury is among the most potentially toxic species to which human populations are exposed, both at high levels through poisonings and at lower levels through consumption of fish and other seafood. However, the molecular mechanisms of methylmercury toxicity in humans remain poorly understood. We used synchrotron X-ray absorption spectroscopy (XAS) to study mercury chemical forms in human brain tissue. Individuals poisoned with high levels of methylmercury species showed elevated cortical selenium with significant proportions of nanoparticulate mercuric selenide plus some inorganic mercury and methylmercury bound to organic sulfur. Individuals with a lifetime of high fish consumption showed much lower levels of mercuric selenide and methylmercury cysteineate. Mercury exposure did not perturb organic selenium levels. These results elucidate a key detoxification pathway in the central nervous system and provide new insights into the appropriate methods for biological monitoring.

Dose-response relationship for human fetal exposure to methylmercury.

Eighty-four Iraqi mothers and their infants had been exposed to methylmercury during pregnancy. The methylmercury had been ingested as a fungicide. Peak maternal hair mercury concentrations were related to the frequency of maternal symptoms during pregnancy and to neurological effects in the infants. These include various degrees of psychomotor retardation. Severe neurological deficits were observed in five children whose maternal peak hair mercury concentrations were 165 to 320 ppm. Minimal symptoms were reported for mothers and children when peak maternal hair levels were below 68 ppm. Minimal clinical neurological signs occurred in children when peak maternal hair mercury concentrations were at an undetermined point between 68 and 180 ppm. Greater fetal risk appears to be associated with exposure during the second trimester. This exposure to methylmercury was acute and the results may not be extrapolated to a constant level of exposure throughout pregnancy. The effects of fetal exposure to methylmercury in marine fish may differ.