Putting findings from the Seychelles Child Development Study into perspective: The importance of a historical special issue of the Seychelles Medical and Dental Journal.

We are pleased to introduce this special issue of Neurotoxicology. It reproduces Volume 7, Number 1 of the Seychelles Medical and Dental Journal (SMDJ), initially published in November 2004. Publication of the SMDJ was discontinued in 2005 and the manuscripts it published are no longer accessible to the scientific community. The papers in this special issue lay the background for the Seychelles Child Development Study (SCDS) and provide valuable data on the MeHg exposures that occurred at Niigata, Japan. They are relevant to the ongoing debate over whether the consumption of fish and consequently low-level exposure to methylmercury (MeHg) is a risk to human health.

Associations between maternal inflammation during pregnancy and infant birth outcomes in the Seychelles Child Development Study.

PROBLEM: Markers of maternal inflammation may determine infant birth outcomes. METHOD OF STUDY: Maternal serum samples were collected at 28 weeks gestation (n = 1418) in the Seychelles Child Development Study Nutrition Cohort 2 and analyzed for immune markers by MSD multiplex assay, including cytokines from the Th1 (IFN-γ, IL-1ß, IL-2 and TNF-α) and Th2 (IL-4, IL-5, IL-10) subsets, with IL-6, MCP-1, TARC, sFlt-1 and VEGF-D. Associations of log-transformed immune markers with birthweight, length, head circumference and gestational age were assessed by multiple linear regression models, which were adjusted for maternal age, BMI, parity, child sex, gestational age and socioeconomic status. RESULTS: Neither total Th1, Th2 nor Th1:Th2 were significantly associated with any birth outcome. However, the angiogenesis marker VEGF-D was predictive of a lower birthweight, (ß = -0.058, P = 0.017) and birth length (ß = -0.088, P = 0.001) after adjusting for covariates. Higher concentrations of CRP were predictive of a lower birthweight (ß = -0.057, P = 0.023) and IL-2 (ß = 0.073, P = 0.009) and the chemokine MCP-1 (ß = 0.067, P = 0.016) were predictive of a longer gestational age. CONCLUSIONS: In our cohort of healthy pregnant women, we found no evidence for associations between the Th1 or Th2 inflammatory markers with birth outcomes. However, VEGF-D and CRP appear to predict lower birthweight and IL-2 and MCP-1 a longer gestation. Greater understanding is required of the variation in these immune markers at different gestational stages, as well as the factors which may regulate their balance in healthy pregnancy. n = 233.

Functional impairment severity is associated with health status among older persons with intellectual disability and cerebral palsy.

BACKGROUND: Studies have noted high rates of specific health disorders in adults with cerebral palsy (CP). However, it remains unclear how growing older with a lifelong neuromotor physical disability confers risk for health outcomes in adults who have both intellectual disability (ID) and CP. AIM: To assess the relationship between health status in older adults with ID either with or without coincident diagnoses of CP. METHOD: Health status data were drawn from 1373 adults aged 33 to 79 years with ID living in small group homes in New York State. Their health status was defined by the presence of common health disorders. Of these, 177 subjects had coincident CP. Prevalence data for nine diseases representing different organ systems were obtained and compared in individuals with and without CP. A Severity of Functional Impairment Index (SFII) was developed based on subjects' capabilities in activities of daily living (ADLs) and mobility. Two logistic regression analyses were conducted to determine if CP diagnosis was an independent predictor of health disorder prevalence, or rather exerted effects similar to those without CP via severity of functional impairment as determined by SFII scores. In addition, older age, gender, and severity of intellectual disability were examined as predictors of health disorder prevalence in all study subjects. RESULTS: Individuals with CP had higher frequencies in four out of the nine health disorders (overweight/obesity, gastroesophageal reflux, urinary tract infections and dysphagia). Analysis revealed a statistically significant association between SFII score and CP diagnosis. CP diagnosis alone was a statistically significant predictor for all of the above four common disorders; however, after adjustment for SFII score was included in health disorder models, only dysphagia showed an independent correlation with a CP diagnosis. CONCLUSION: With the exception of dysphagia, impairment in ADLs and walking capabilities, and not CP diagnosis alone, accounted for disparities in specific diseases. Although the diagnosis of CP may be correlated with functional impairment, it alone may play a minor role in determining health trajectories in older persons with conjoint ID and CP.

Habitual fish consumption does not prevent a decrease in LCPUFA status in pregnant women (the Seychelles Child Development Nutrition Study).

Information on the status of long-chain polyunsaturated fatty acids (LCPUFAs) in pregnancy and breast milk in very high fish-eating populations is limited. The aim of this study was to examine dietary intake and changes in fatty acid status in a population of pregnant women in the Republic of Seychelles. Serum docosahexaenoic acid (DHA) decreased significantly between 28-week gestation and delivery (n=196). DHA status did not correlate significantly with length of gestation and was not associated with self-reported fish intake, which was high at 527 g/week. In breast milk, the ratio of DHA to arachidonic acid (AA) was consistent with those observed in other high fish-eating populations. Overall the data suggest that high exposure to LCPUFAs from habitual fish consumption does not prevent the documented decrease in LCPUFA status in pregnancy that occurs as a result of foetal accretion in the third trimester of pregnancy.

Does methylmercury have a role in causing developmental disabilities in children?

Methylmercury (MeHg) is a potent neurotoxin that in high exposures can cause mental retardation, cerebral palsy, and seizures. The developing brain appears particularly sensitive to MeHg. Exposure levels in pregnant experimental animals that do not result in detectable signs or symptoms in the mother can adversely affect the offspring's development. Studies of human poisonings suggest this may also occur in humans. Human exposure to MeHg is primarily dietary through the consumption of fish: MeHg is present in all fresh and saltwater fish. Populations that depend on fish as a major source of dietary protein may achieve MeHg exposure levels hypothesized to adversely affect brain development. Increasing mercury levels in the environment have heightened concerns about dietary exposure and a possible role for MeHg in developmental disabilities. Follow-up studies of an outbreak of MeHg poisoning in Iraq revealed a dose-response relationship for prenatal MeHg exposure. That relationship suggested that prenatal exposure as low as 10 ppm (measured in maternal hair growing during pregnancy) could adversely affect fetal brain development. However, using the same end points as were used in the Iraq study, no associations have been reported in fish-eating populations. Using a more extensive range of developmental end points, some studies of populations consuming seafood have reported associations with prenatal MeHg exposure, whereas others have found none. This paper reviews the data presently available associating MeHg exposure with development and poses some of the unanswered questions in this field.

Prenatal methylmercury exposure and children: neurologic, developmental, and behavioral research.

Mercury is present in the earth's crust and is methylated by bacteria in aquatic environments to methylmercury (MeHg). It is then concentrated by the food chain so predatory fish and sea mammals have the highest levels. Thus, consuming seafood leads to exposure. MeHg readily crosses the placenta and the blood-brain barrier and is neurotoxic. The developing fetal nervous system is especially sensitive to its effects. Prenatal poisoning with high dose MeHg causes mental retardation and cerebral palsy. Lower level exposures from maternal consumption of a fish diet have not been consistently associated with adverse neurodevelopmental outcomes. However, most studies have considerable uncertainty associated with their results. Two large controlled longitudinal studies of populations consuming seafood are underway that are likely to determine if any adverse effects can be identified. No adverse associations have been found in the Seychelles, where exposure is mainly from fish consumption. In the Faroe Islands where exposure is primarily from consumption of whale meat and not fish, adverse associations have been reported. The Seychelles population consumes large amounts of marine fish containing MeHg concentrations similar to commercial fish in the United States. Current evidence does not support the hypothesis that consumption of such fish during pregnancy places the fetus at increased neurodevelopmental risk.

Benchmark concentrations for methylmercury obtained from the Seychelles Child Development Study.

Methylmercury is a neurotoxin at high exposures, and the developing fetus is particularly susceptible. Because exposure to methylmercury is primarily through fish, concern has been expressed that the consumption of fish by pregnant women could adversely affect their fetuses. The reference dose for methylmercury established by the U.S. Environmental Protection Agency was based on a benchmark analysis of data from a poisoning episode in Iraq in which mothers consumed seed grain treated with methylmercury during pregnancy. However, exposures in this study were short term and at much higher levels than those that result from fish consumption. In contrast, the Agency for Toxic Substances and Disease Registry (ATSDR) based its proposed minimal risk level on a no-observed-adverse-effect level (NOAEL) derived from neurologic testing of children in the Seychelles Islands, where fish is an important dietary staple. Because no adverse effects from mercury were seen in the Seychelles study, the ATSDR considered the mean exposure in the study to be a NOAEL. However, a mean exposure may not be a good indicator of a no-effect exposure level. To provide an alternative basis for deriving an appropriate human exposure level from the Seychelles study, we conducted a benchmark analysis on these data. Our analysis included responses from batteries of neurologic tests applied to children at 6, 19, 29, and 66 months of age. We also analyzed developmental milestones (age first walked and first talked). We explored a number of dose-response models, sets of covariates to include in the models, and definitions of background response. Our analysis also involved modeling responses expressed as both continuous and quantal data. The most reliable analyses were considered to be represented by 144 calculated lower statistical bounds on the benchmark dose (BMDLs; the lower statistical bound on maternal mercury hair level corresponding to an increase of 0.1 in the probability of an adverse response) derived from the modeling of continuous responses. The average value of the BMDL in these 144 analyses was 25 ppm mercury in maternal hair, with a range of 19 to 30 ppm.

Semiparametric modeling of age at achieving developmental milestones after prenatal exposure to methylmercury in the Seychelles child development study.

Controversy exists concerning the fetal risk associated with exposure to low-dose methylmercury from maternal fish consumption. Previous studies of the effects of acute prenatal mercury exposure identified delays in achieving developmental milestones among exposed children. This led to public health concern that prenatal low-dose exposure from fish consumption could adversely affect the fetus. We evaluated the effects of prenatal methylmercury exposure (through maternal fish consumption) on the age that children walked and first said words in the main study cohort of the Seychelles Child Development Study. We used semiparametric generalized additive models to identify nonlinearities in the relationships between prenatal exposure and developmental outcomes, after adjusting for covariates, and to evaluate their importance. Very slight delays (<1 day) in walking were seen as mercury levels increased from 0 to 7 ppm, but this effect did not persist at the higher exposure levels represented by the cohort, making it difficult to conclude that a cause and effect relationship existed at the exposure levels seen in this cohort. There was no evidence for any association between prenatal exposure and age at talking.

Effects of providing comprehensive ambulatory services to children with chronic conditions.

OBJECTIVE: To document the effects of a comprehensive program of care on the resource utilization and cost of care for children with chronic conditions. DESIGN: Descriptive study of 10715 admissions between 1984 and 1995 with analyses of costs based on charges. Comparisons were made with data from a national consortium of academic medical centers and from a national survey of hospitals. A 2-week survey of staff was conducted to identify their use of time in the care of these patients. PATIENTS: Children aged birth through 18 years meeting International Classification of Diseases, Ninth Revision, Clinical Modification criteria for chronic conditions. Patients with acute conditions were used as controls. INTERVENTION: A program of expanded care funded since 1989 by a regional insurance company. RESULTS: Between 1984 and 1995, mean length of stay for children with chronic conditions decreased from 83.9 to 10.6 days; mean annual admissions decreased from 2796 to 1622. Median hospital inpatient charges, adjusted for cost of living, decreased from $26.1 to $14.6 million. A $77.7 million savings occurred for inpatient care, with total expenditures from the insurance program of $3.6 million (a 21:1 ratio). Almost half the professional activities provided for these children were for services that could not be reimbursed in a fee-for-service model. Median adjusted inpatient charges were lower in Rochester, NY ($8746) than in other academic medical centers ($12773) or in a national survey of hospitals ($12462), and fewer children were readmitted within 30 days in Rochester (12.7%) than in other academic medical centers (15.0%). CONCLUSIONS: An investment of funds by a regional insurance company was associated with reduced costs, admissions, and lengths of stay for children with chronic conditions, and resulted in significant savings for the company. This model may be applicable to other centers.

A review of methylmercury and child development.

Methylmercury (MeHg) is a neurotoxin present in both fresh and saltwater fish throughout the world. Increased levels of MeHg can be found in individuals who regularly consume fish. The developing brain is very sensitive to the deleterious effects of MeHg, and prenatal exposure can occur when the mother has a diet high in fish. If the level of MeHg exposure achieved by eating fish adversely affects the fetus or child's neurological development it could have far reaching public health implications. Studies of human prenatal MeHg poisoning in Iraq suggest that MeHg levels achieved by eating fish may affect neurological development even when the fish MeHg levels are not elevated by obvious pollution. Studies in fish eating populations have identified adverse neurological and developmental outcomes, but these findings have not been consistent. Additional studies are presently underway to determine whether consistent adverse outcomes can be identified using more sensitive testing methods and examining children older than in previous studies. This review examines studies of human prenatal and postnatal MeHg exposure. Studies of poisoning episodes where children are symptomatic and studies of fish eating populations where no symptoms are apparent will be addressed. Individuals around the world depend on fish as a protein source and increasing evidence suggests that regular fish consumption has cardiovascular benefits. It is not presently clear whether MeHg exposures from a high fish diet adversely affect children's neurological development, but it is an important question to answer.

The Seychelles study of fetal methylmercury exposure and child development: introduction.

Studies of outbreaks of methylmercury poisoning in Japan and Iraq from consumption of methylmercury (MeHg)-contaminated fish or bread proved that brain was the target organ, the toxic effects were dose-related, and the fetal brain was especially susceptible. Previous population studies suggested that a 5% risk of minimal fetal effect may be associated with a maternal hair mercury concentration during pregnancy of 10-20 ppm (mu g/g), a level that can be readily achieved by frequent consumers of fish. However, these studies had limitations, and as a result no definite conclusion concerning the lowest effect level could be reached and the question of a possible hazard to public health remained unanswered. There was a clear need for a more definitive study that would be prospective, involve a large enough cohort for risk analysis and adhere to accepted epidemiological principles. An appropriate site for such a study is the Republic of Seychelles, a location that afforded successful collaboration between the Seychelles Ministry of Health and faculty of the University of Rochester. A pilot study of 804 infant-mother pairs was followed by a main study of 779 mother-infant pairs. In the pilot study children were examined once between 5 and 109 weeks of age; in the main study they are being evaluated longitudinally starting at 6 1/2 months of age. This paper introduces both the pilot and main studies, describes their design, and summarizes the findings through 6 1/2 months of age. When the Seychelles study is completed, the analyses will provide a database for those nations that choose to regulate their citizens' fish consumption and/or provide dietary education.

Neurodevelopmental outcomes of Seychellois children sixty-six months after in utero exposure to methylmercury from a maternal fish diet: pilot study.

The Seychelles Child Development Study (SCDS) is testing the hypothesis that prenatal exposure to low concentrations of methylmercury from a maternal diet high in fish is related to the child's developmental outcome. In this report, 217 children from a pilot cohort were reevaluated at 66 months of age. The evaluation included the McCarthy Scales of Children's Abilities, the Preschool Language Scale, and age-appropriate sub-tests from the Woodcock-Johnson Tests of Achievement. Maternal hair total mercury, measured by cold vapor atomic absorption in a maternal hair segment corresponding to pregnancy, revealed a median exposure of 7.1 ppm. The association between maternal hair mercury levels and neurodevelopmental outcomes at 66 months of age was examined by multiple linear regression analysis with adjustment for important confounding variables. The results indicated that mercury exposure was negatively associated with four endpoints (the McCarthy General Cognitive Index and Perceptual Performance subscale and The Preschool Language Scale Total Language and Auditory Comprehension subscale). After normalizing the data by removal of a small number of outliers or highly influential scores, the mercury effects were no longer significant except for auditory comprehension. These results should be viewed as preliminary and interpreted with caution, since the SCDS main study 66-month evaluations, which are better controlled with more detailed endpoints are being analyzed. This study highlights the difficulties in interpreting epidemiologic studies of this type and the degree to which overall results in multivariate analyses can be influenced by a very small number of cases.

Main neurodevelopmental study of Seychellois children following in utero exposure to methylmercury from a maternal fish diet: outcome at six months.

Methylmercury (MeHg) is a human neurotoxin to which the developing fetal brain is especially sensitive. The lowest dose of MeHg that impairs neurodevelopment in the human fetus is not known. The Seychelles Child Development Study (SCDS) is testing the hypothesis that fetal MeHg exposure from a maternal diet high in oceanic fish is related to child neurodevelopmental outcomes. Fish is the major protein source in the Republic of Seychelles, where a cohort of 779 mother-infant pairs was enrolled in a prospective longitudinal study. Maternal total hair mercury values during pregnancy were determined by cold vapor atomic absorption and ranged from 0.5 ppm to 26.7 ppm with a median of 5.9 ppm. When the children were 6 1/2 months of age, an examiner blinded to the maternal mercury value performed a neurological examination, the Fagan test of visual recognition memory, and the Denver Developmental Screening Test-Revised (DDST-R). On the DDST-R 2% scored other than normal while 3.4% had an overall neurological score other than normal. The Fagan test of visual recognition memory showed a median score of 60.5%, and the Rose attention measure from that test showed a median score of 37.9. The association between fetal mercury exposure and neurodevelopmental endpoints was examined by multiple regression analyses. After adjusting for covariates, no association between the maternal hair mercury level during pregnancy and an adverse neurodevelopmental outcome of the child was identified at 6 1/2 months of age.

Neurodevelopmental test selection, administration, and performance in the main Seychelles child development study.

The Seychelles Child Development Study was designed to provide data on normal neurodevelopment of Seychellois children and to examine the relationship of their neurodevelopmental outcomes to in utero fetal exposure to low concentrations of methylmercury from a maternal diet high in fish. This paper outlines the strategies used to select, modify, and field test evaluation tools used in the main longitudinal prospective study of 740 children (95% of the cohort of 779 initially enrolled in 1989). It also gives population statistics and quality assurance data for the tests administered and the evaluation of the home environments.

An analysis of autopsy brain tissue from infants prenatally exposed to methymercury.

Brains from 32 neonatal autopsies from the Seychelles were examined histologically and analyzed for mercury levels. Six brain regions were sampled: frontal and occipital cortex, temporal cortex with hippocampus, basal ganglia with thalamus, cerebellum, and pons with medulla. Tissue blocks for histology and mercury analysis were taken from opposing faces to provide for correlation of findings. Similar studies were performed on 12 reference neonatal brains from Rochester, New York. No clear-cut developmental abnormality was found, but some brains exhibited low-grade, non-specific destructive changes. Total mercury levels, most of it in the organic form, were elevated in many of the Seychelles specimens. No correlation was demonstrated between mercury levels and degree or type of histologic change. There was considerable variability in total mercury for each anatomic region among the 32 Seychelles cases, as well as from one region to another in individual brains. All values of total mercury were under 300 ppb. Statistical analysis of mean mercury levels for each region demonstrated higher values in deep subcortical nuclei, brain stem, and cerebellum, phylogenetically older parts of the brain. When total mercury concentration of each region was paired with all other areas in the same brain and the paired values plotted for the entire group of brains, high correlations were obtained for all brain pairs, suggesting a strong concentration-dependent relationship between mercury intake and brain content. Analysis of mercury levels in separately dissected blocks of grey and white matter from 12 specimens revealed no significant differences between grey and white. In comparison with other human developmental studies and with experimental developmental studies in animals, where toxicity has been demonstrated with total mercury brain levels above 1,000 ppb, this study found no evidence of toxicity within a range of mercury levels below 300 ppb. Submicroscopic changes, subcellular alterations, subtle disturbances in the unfolding of brain architectonics -- none of these are excluded with methods used in this report. Further studies of threshold effects of MeHg on fetal brain are essential. That approximately half of the mercury resides in glial elements in white matter reinforces the need to focus attention upon glia as well as neurons during development.

Effects of prenatal methylmercury exposure from a high fish diet on developmental milestones in the Seychelles Child Development Study.

Mercury is widespread in the environment and exists in several physical and chemical forms. Prenatal exposure to methylmercury disrupts brain development. The most common mode of prenatal methylmercury exposure is maternal fish consumption. Studies of human prenatal exposure in Iraq following maternal ingestion of methylmercury treated grain suggested that maternal hair mercury concentrations above 10 ppm may be related to delayed developmental milestones and neurological abnormalities. This level of exposure can be achieved by frequent consumption of fish. The Seychelles Child Development Study analyzed developmental milestones similar to those determined in Iraq in a large controlled, prospective study of children exposed prenatally to methylmercury when their mothers ate fish. As part of this ongoing study, cohort children were evaluated at 6.5, 19, 29, and 66 months of age. At 19 months care-givers were asked at what age the child walked (n=720 out of 738) and talked (n=680). Prenatal mercury exposure was determined by atomic absorption analysis of maternal hair segments corresponding to hair growth during the pregnancy. The median mercury level in maternal hair was 5.8 ppm with a range of 0.5-26.7 ppm. The mean age (in months) at walking was 10.7 (SD = 1.9) for females and 10.6 (SD = 2.0) for males. The mean age at talking (in months) was 10.5 (SD = 2.6) for females, and 11.0 (SD = 2.9) for males. After adjusting for covariates and statistical outliers, no association was found between the age at which Seychellois children walked or talked and prenatal exposure to mercury. Normal ages at achievement of the developmental milestones walking and talking were found in Seychellois toddlers following prenatal exposure to methylmercury from a maternal fish diet. These results do not support the lowest effect levels in young children following prenatal methylmercury exposure predicted by the dose response analysis of the Iraq data. More detailed studies in older children are needed to determine if there are adverse effects in fish eating populations.

Evaluation of techniques for assessing neurobehavioral development in children.

A battery of tests has been designed to explore functional disabilities in children 10-12 years of age arising from adverse conditions during early development. At these ages, it becomes possible to use more complex and challenging tests than those typically used at earlier ages. Although the battery was prompted originally by questions arising from methylmercury exposure, it was also designed for applicability to neurotoxicant exposures arising from pesticides, solvents, persistent organic pollutants such as PCBs and dioxins, other metals, and nutrient excesses and deficiencies as well. The test battery includes the following categories: (1) neuropsychological tests with established psychometric properties not widely exploited in studies of developmental neurotoxicity; (2) electrophysiological and behavioral tests of sensory functioning spanning a broader range of indices than those used generally in studies of neuropsychological development; and (3) adaptations of performance tasks used previously only in animals. The battery was developed in Rochester, New York, and then field-tested on a group of 61 children in the Republic of the Seychelles, where the Ministry of Health had established the Child Development Center. Our findings suggest a number of tests and procedures with the potential for inclusion in test batteries aimed at the exploration of adverse neurodevelopmental effects.

The Seychelles child development study on neurodevelopmental outcomes in children following in utero exposure to methylmercury from a maternal fish diet: background and demographics.

Studies in Japan showed that fetal exposure to methylmercury during pregnancy can lead to severe neurodevelopmental changes in the infant while the mother suffers no or minimal effects. Fish contains methylmercury and there is concern that adverse neurodevelopmental effects may occur secondary to low-dose methylmercury exposure in utero from maternal fish consumption. The Seychelles Child Development Study has been examining the relationship between prenatal exposure to methylmercury during pregnancy in a population with high fish consumption and the neurodevelopmental outcome. Over 80% of Seychellois women eat fish daily, and the median fish meals per week during pregnancy is 12. Following a pilot study of 804 mother-infant pairs, a longitudinal main study of another 779 mother-infant pairs was initiated. The main study design includes collection of educational and socioeconomic information about the family and periodic standardized neurodevelopmental tests at specific ages from 6 1/2 months to 66 months of age. In this paper, we describe the background to the studies and give demographic characteristics of both the pilot and main study cohorts.