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.

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.

The biological monitoring of mercury in the Seychelles study.

The concentration of total mercury in maternal hair during pregnancy was used as a measure of fetal exposure to methylmercury in a study of a fish-eating population in the Seychelles islands. A segment of scalp hair approximately 10 centimeters in length, that grew during pregnancy, was selected for measurement. Total and inorganic mercury were measured by cold vapor atomic absorption (CVAA) using the Magos reagents (Magos, 1971). For comparative purposes, total mercury was measured by X-ray Fluorescent Spectrometry (XRF) and methylmercury by gas chromatography/atomic fluorescence detection (GC/AFD) in a subset of hair samples. A limited number of fish samples were also analyzed. Extensive interlaboratory testing was conducted to ensure accuracy of the mercury measurements. Concentrations of organic mercury calculated as the difference between total and inorganic mercury as measured by CVAA agreed with those of methylmercury measured on the same samples of hair by GC/AFD. Methylmercury measured by GC/AFD and organic mercury measured by CVAA accounted for over 80% of the total mercury in hair and over 90% of the total mercury in fish muscle. To test the accuracy of recapitulation by hair sampling, hair samples were collected from mothers at the time of delivery and 6 months later. The segment corresponding to the pregnancy term was selected for measurement assuming a hair growth rate of 1.1 cm/month. Results from both samples were in close agreement. As part of both a pilot investigation followed by the main study, maternal hair samples were collected each year from 1986 to 1989 for a total of 1604 samples. The median and mean values for each year's collection fell in the range of 5.9 to 8.2 ppm and exhibited no statistically significant trend with time. The highest recorded concentration was 36 ppm. In hair samples from 654 mothers, the mean concentration of total mercury was compared with the mean concentrations in segments corresponding to each trimester, approximately 3.3 centimeters in length. A high degree of correlation was found between mean levels in each trimester versus the entire pregnancy segment.

A pilot neurodevelopmental study of Seychellois children following in utero exposure to methylmercury from a maternal fish diet.

It is not known if fetal neurodevelopmental damage occurs in humans at the low-level methylmercury exposure achieved by eating fish. To address this question, a cohort of 804 children in the Republic of Seychelles was identified who had fetal methylmercury exposure from a maternal diet high in oceanic fish. Mercury was determined by measuring the maternal total hair mercury during pregnancy, a standard index of methylmercury exposure. The median fetal mercury exposure was 6.6 ppm. Children were evaluated once between 5 to 109 weeks of age. Testing included the revised Denver Developmental Screening Test (DDST-R) and a neurological examination. The association between maternal hair mercury levels and developmental outcome was evaluated by multiple logistic regression analysis. Covariates for the child included gender, birth weight, one and five-minute Apgar score, age at testing, and medical problems, and, for the mother, age, tobacco and alcohol consumption during pregnancy, and medical problems. An association between fetal mercury exposure and development was found when DDST-R scores of questionable and abnormal were combined, a procedure used by previous investigators. These results should be viewed with caution since the association disappeared when DDST-R scores of questionable were treated in the standard manner as passes.

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.

Longitudinal neurodevelopmental study of Seychellois children following in utero exposure to methylmercury from maternal fish ingestion: outcomes at 19 and 29 months.

UNLABELLED: Despite the importance of defining developmental consequences for humans of in utero exposure to low levels of methylmercury, it is not yet clear if there are postnatal effects in fish-eating populations. The Seychelles Child Development Study (SCDS), now underway in the Republic of Seychelles, is following children to test the hypothesis that prenatal exposure to low concentrations of MeHg through maternal ingestion of fish is related to child development outcomes. In this study, children were evaluated with the Bayley Scales of Infant Development (BSID) at 19 mos. of age (N = 738). The cohort was evaluated again at 29 mos. (N = 736) with the BSID and the Bayley Infant Behavior Record. Mercury exposure determined by cold vapor atomic absorption analysis of maternal hair segments corresponding to pregnancy revealed a median exposure of 5.9 ppm (Range 0.5 - 26.7 ppm). The association between maternal hair mercury concentrations and neurodevelopmental outcomes at 19 and 29 mo. of age was examined by multiple regression analysis with adjustment for confounding variables. RESULTS: BSID Intertester reliability was ascertained by the Kappa statistic and was high. The mean BSID Mental Scale Indexes at both 19 and 29 mo. were comparable to the mean performance of US children. The mean BSID Psychomotor Scale Indexes at 19 and 29 mo. were 2 SD units above US norms, but consistent with previous findings of motoric precocity in children reared in African countries. No effect of mercury was detected on BSID scores at either age. On the Bayley Infant Behavior Record, activity level in boys, but not girls, decreased with increasing mercury exposure. Only one subjective endpoint was correlated with prenatal exposure to mercury. This study may have implications for environmental health policies concerning mercury in fish or fish consumption during pregnancy. Follow-up data are needed to determine if adverse effects occur at older ages and if such effects are determined to be related to mercury.

Monitoring methylmercury during pregnancy: maternal hair predicts fetal brain exposure.

Autopsy brains were obtained from infants dying from a variety of causes within a few days of birth in a population exposed to methylmercury in fish. Infant and maternal blood and hair samples were also obtained. The concentration of total mercury in 6 major brain regions were highly correlated with maternal hair levels. This correlation was confirmed by a sequence of comparisons of maternal hair to maternal blood to infant blood and finally to infant brain. The results lend support to the use of maternal hair in assessing fetal exposure to methylmercury in fish-eating populations.

Summary of the Seychelles child development study on the relationship of fetal methylmercury exposure to neurodevelopment.

The Seychelles Child Development Study is examining the association between fetal methylmercury exposure from a maternal diet high in fish and subsequent child development. The study is double blind and uses maternal hair mercury as the index of fetal exposure. An initial cross-sectional pilot study of 804 infants aged 1 to 25 months suggested that mercury may affect development. A follow up of 217 pilot children at 66 months of age also suggested that neurodevelopmental effects might be present, but the result was dependent on outcomes in a small number of children. On the basis of initial results in the pilot study a prospective, longitudinal main study with more covariates and expanded endpoints was begun on a new cohort of 779 children. No association with neurodevelopment was seen at 6 1/2, 19, or 29 months of age, but there was an inverse relationship at 29 months in boys only between mercury level and activity as judged by the examiner. Adverse neurodevelopmental effects from fetal mercury exposure in the pilot study are highly dependent on how the data are analyzed and no definite effects have been detected through 29 months of age in the main study. In a related study, 32 brains were obtained at autopsy from Seychellois infants. These were examined histologically and analyzed for mercury. No clear histological abnormalities were found. Mercury levels ranged from a background of about 50 ppb up to 300 ppb, and correlated well between brain regions. For 27 brains maternal hair from delivery was available and hair mercury correlated well with brain mercury.

Fetal methylmercury study in a Peruvian fish-eating population.

Maternal consumption during pregnancy of methylmercury (MeHg)-contaminated fish in Japan and of MeHg-contaminated bread in Iraq caused psychomotor retardation in the offspring. Studies in Iraq suggested adverse fetal effects when maternal hair mercury concentrations were as low as 20 ppm. This prospective study involved 131 infant-mother pairs in Mancora, Peru with peak maternal hair MeHg levels during pregnancy from 1.2 ppm to 30.0 ppm, geometric mean 8.3. The MeHg was believed to be derived from marine fish in the diet. There was no increase in the frequency of neurodevelopmental abnormalities in early childhood. The possible role of selenium or other protective mechanisms in marine fish is discussed. This previously unpublished study was conducted between 1981 and 1984. Our report of August 1985 to the funding agencies has been circulated, and the data were presented at the Twelfth International Neurotoxicology Conference in Hot Spring, Arkansas, October 30 to November 2, 1994. The current account has not been modified or updated since 1985. For reference to interim publications on fetal MeHg studies in Iraq and New Zealand see Marsh et al., 1995.

Mononeuritis multiplex and vasculitis. Association with anti-neutrophil cytoplasmic autoantibody.

Mononeuritis multiplex is known to occur in many illnesses including certain types of systemic vasculitis. Anti-neutrophil cytoplasmic autoantibody (ANCA) has been described in association with Wegener's granulomatosis, polyarteritis nodosa, pauci-immune necrotizing crescentic glomerulonephritis, and so-called ANCA-associated vasculitis. We describe three patients who presented with mononeuritis multiplex and positive tests for ANCA. A careful search revealed underlying vasculitis in two of the three patients. Whereas both respiratory and renal involvement are well known in ANCA-associated vasculitis, to our knowledge the relationship of mononeuritis multiplex and ANCA positivity has not previously been described. The three patients were treated with steroids and oral cyclophosphamide. All demonstrated marked clinical improvement, as well as a decrease or disappearance of the ANCA. Since mononeuritis multiplex may be a presenting symptom of many illnesses, a serological marker may be helpful for early diagnosis and prompt treatment.

Dose-response analysis of infants prenatally exposed to methyl mercury: an application of a single compartment model to single-strand hair analysis.

A new method of estimating fetal exposure is used in a dose-response analysis of data from the 1971 outbreak of methyl mercury poisoning in rural Iraq. An X-ray fluorescence instrument for the measurement of single strands of human hair was employed to obtain longitudinal profiles recapitulating fetal exposure. Logit and hockey-stick models as well as nonparametric smoothing are used to describe data on delayed development and central nervous system abnormality.

Repeated suicide attempts by the intravenous injection of elemental mercury.

The case of a patient who repeatedly injected himself intravenously with elementary mercury in suicide attempts is presented and the toxicological effects of this chemical form and route of exposure of mercury are examined. A review of the literature reveals that elemental mercury, when injected as opposed to inhaled, causes few of the effects typical of mercurialism; pleuritic chest pain was frequently reported, whereas renal and central nervous system involvement were less common. Evidence of premorbid psychiatric disturbances was found in ten of fourteen non-cardiac catheterization exposures to intravenous elemental mercury. Findings in our patient were consistent with these observations. One additional and noteworthy finding in our case was that documented deposits of elemental mercury in the right parietal lobe of the brain did not correlate with any specific deficits on neuropsychological testing. Consultation-liaison psychiatry plays an important role in the treatment and care of these complex patients.

Fetal methylmercury poisoning. Relationship between concentration in single strands of maternal hair and child effects.

Pregnant women consumed bread that was prepared from methylmercury-treated wheat. Single strands of maternal head hair were analyzed by x-ray fluorescence spectrometry. The index of fetal exposure was the maximum hair mercury concentration during gestation. Effects were measured by the frequency of psychomotor retardation, seizures, and neurological signs in the children. A dose-response relationship was demonstrated for fetal effects of methylmercury. Analysis of single hair strands provides a better index of acute or subacute fetal exposure than analysis of bundles of hair; the duration and degree of exposure are more accurately defined. A sex difference in response is discussed.

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.

Methylmercury in populations eating large quantities of marine fish.

A Peruvian population was identified that was chronically exposed to methylmercury from the long-term consumption of ocean fish. The weekly fish intake averaged 10.1 kg per average family of 6.2 persons. Blood methylmercury concentrations ranged from 11 to 275 ng/ml, with a mean of 82 ng/ml. Paresthesias were reported by 29.5% of the population. In contrast, a nearby control population had a mean weekly fish consumption of 1.9 kg per average family of 6.4 persons. Their blood methylmercury levels were 3.3-25.1 ng/ml, with a mean of 9.9 ng/ml. Paresthesias were reported by 49.5% of this control group. No individual was identified with symptoms or signs that could be attributed to methylmercury intoxication.

Fetal methylmercury poisoning: clinical and toxicological data on 29 cases.

This report describes psychomotor retardation in infants caused by prenatal exposure to methylmercury. A study of 29 mother-infant pairs established a relationship between maximum maternal hair mercury concentration during pregnancy and the frequency of neurological effects in the infants. The latter included delayed achievement of developmental milestones with or without neurological signs. The infants were 4 1/2 to 5 years of age on last examination. Ten infants of mothers who had maximum hair concentrations in the range of 99 to 384 pars per million (ppm) had a significantly higher frequency of abnormal findings than those in two groups having lower maternal hair mercury concentrations (12 to 85 and 0 to 11 ppm). The group sizes were too small to allow identification of a specific "threshold" maternal hair concentration above which such effects can be expected. Transient paresthesias during pregnancy occurred in 80% of the mothers in the higher concentration group (99 to 384 ppm) as compared with 30% and 22% in the lower groups. Neurological abnormalities were found in some children whose mothers had been asymptomatic during pregnancy.