succimer and Child-Behavior-Disorders

Because the toxicological effects of mercury (Hg) are more serious in the developing central nervous system of children than adults, there are growing concerns about prenatal and early childhood Hg exposure. This study examined postnatal methylmercury (MeHg) exposure and cognition and behavior in 780 children enrolled in the Treatment of Lead (Pb)-exposed Children clinical trial (TLC) with 396 children allocated to the succimer and 384 to the placebo groups. Mercury exposure was determined from analyses of blood drawn 1 week before randomization and 1 week after treatment began when succimer had its maximal effect on blood Pb (PbB). The baseline MeHg concentrations were 0.54 microg/L and 0.52 microg/L and post-treatment concentrations were 0.51 microg/L and 0.48 microg/L for placebo and succimer groups, respectively. Because the baseline characteristics in the two groups were balanced and because succimer had little effect on MeHg concentration and no effect on the cognitive or behavioral test scores, the groups were combined in the analysis of MeHg and neurodevelopment. The children's IQ and neurobehavioral performance were tested at age 2, 5 and 7 years. We saw weak, non-significant but consistently positive associations between blood MeHg and IQ test scores in stratified, spline regression and generalized linear model data analyses. The behavioral problem scores were constant or decreased slightly with increasing MeHg concentration. Additional adjustment for PbB levels in multivariable models did not alter the conclusion for MeHg and IQ scores, but did confirm that concurrent PbB was strongly associated with IQ and behavior in TLC children. The effects of MeHg on neurodevelopmental indices did not substantially differ by PbB strata. We conclude that at the present background postnatal MeHg exposure levels of US children, adverse effects on children's IQ and behavior are not detectable.

Topics: Age Factors; Antidotes; Child Behavior Disorders; Child Development; Child, Preschool; Cognition; Cognition Disorders; Female; Humans; Infant; Intelligence; Lead; Lead Poisoning, Nervous System, Childhood; Longitudinal Studies; Male; Mercury Poisoning, Nervous System; Methylmercury Compounds; Neuropsychological Tests; Statistics as Topic; Succimer

Lead exposure in childhood lowers IQ scores, but its effect on children's behavior is less clear. Because IQ, per se, affects behavior, measuring the direct effect of lead requires measuring and then adjusting for IQ. In addition, either peak blood lead concentration, usually at 2 years old, or the lower blood lead level measured at school age may be the most relevant. Few studies have all of this information.. The purpose of this work was to differentiate the direct effect of lead on behavior and the indirect effect through IQ and to examine the strength of the association for peak and concurrent blood lead concentration.. Data come from a clinical trial of the chelating drug succimer to prevent cognitive impairment in 780 urban 12- to 33-month-olds with blood lead concentrations of 20 to 44 microg/dL. The children were followed from ages 2 to 7 years. The trial data were analyzed as a prospective observational study.. Blood lead concentration at 2 years old was not associated with Conners' Parent Rating Scale-Revised scores at 5 years of age or Behavioral Assessment Systems for Children scores at 7 years of age. Blood lead level at 7 years of age had direct effects on the Behavioral Assessment Systems for Children behavioral symptoms index, externalizing, and school problems at age 7.. Concurrent blood lead concentration was associated with externalizing and school problems scales at 7 years of age, and the effect was not entirely mediated through the effect of lead on IQ.

Topics: Age Distribution; Causality; Chelating Agents; Child; Child Behavior Disorders; Child, Preschool; Cognition Disorders; Comorbidity; Environmental Exposure; Environmental Monitoring; Epidemiological Monitoring; Female; Follow-Up Studies; Humans; Intelligence; Lead; Lead Poisoning, Nervous System, Childhood; Male; Odds Ratio; Regression Analysis; Succimer; United States; Urban Population

In one study of children in 27 families with maternal retardation, those children with higher intelligence quotient (IQ) were more likely to have multiple behavior problems than those with lower IQ. If true, this result would affect clinical practice, but it has not been replicated. Because the setting of the initial observation is similar to the setting of childhood lead poisoning, we attempted a replication using data from the Treatment of Lead-Exposed Children (TLC) study, in which 780 children aged 12-33 mo with blood lead levels 20-44 microg/dL were randomized to either succimer treatment or placebo and then followed up to 5 y. Of 656 mothers of TLC children with IQ measured, 113 demonstrated mental retardation (IQ <70). Whether maternal IQ was <70 or >or=70, children with IQ >or=85 were rated more favorably on cognitive tests and behavioral questionnaires than children with IQ <85; these measures included Conners' Parent Rating Scale-Revised at age 5, the Developmental Neuropsychological Assessment at ages 5 and 7, and the Behavioral Assessment System for Children at age 7. Among children of mothers with IQ <70, those with IQ >or=85 did not show more severe clinical behavioral problems, nor were they more likely to show multiple behavior problems. Children with higher IQ have fewer behavior problems, irrespective of the mother's IQ. In the special setting of mothers with IQ <70, children with higher IQ are not at greater risk of behavior problems.

Topics: Achievement; Chelating Agents; Child; Child Behavior Disorders; Child, Preschool; Female; Humans; Intellectual Disability; Intelligence; Intelligence Tests; Lead; Lead Poisoning; Male; Mothers; Neuropsychological Tests; Random Allocation; Social Environment; Succimer; Urban Population