title: Is susceptibility to prenatal methylmercury exposure from fish consumption non-homogeneous? Tree-structured analysis for the Seychelles Child Development Study.
abstract: Studies of the association between prenatal methylmercury exposure from maternal fish consumption during pregnancy and neurodevelopmental test scores in the Seychelles Child Development Study have found no consistent pattern of associations through age 9 years. The analyses for the most recent 9-year data examined the population effects of prenatal exposure, but did not address the possibility of non-homogeneous susceptibility. This paper presents a regression tree approach: covariate effects are treated non-linearly and non-additively and non-homogeneous effects of prenatal methylmercury exposure are permitted among the covariate clusters identified by the regression tree. The approach allows us to address whether children in the lower or higher ends of the developmental spectrum differ in susceptibility to subtle exposure effects. Of 21 endpoints available at age 9 years, we chose the Weschler Full Scale IQ and its associated covariates to construct the regression tree. The prenatal mercury effect in each of the nine resulting clusters was assessed linearly and non-homogeneously. In addition we reanalyzed five other 9-year endpoints that in the linear analysis had a two-tailed p-value <0.2 for the effect of prenatal exposure. In this analysis, motor proficiency and activity level improved significantly with increasing MeHg for 53% of the children who had an average home environment. Motor proficiency significantly decreased with increasing prenatal MeHg exposure in 7% of the children whose home environment was below average. The regression tree results support previous analyses of outcomes in this cohort. However, this analysis raises the intriguing possibility that an effect may be non-homogeneous among children with different backgrounds and IQ levels.
authors.affiliation: Department of Biostatistics and Computational Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA. Lhuang@bst.rochester.edu
authors.forename: Li-Shan
authors.initials: LS
authors.lastname: Huang
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Myers
authors.forename: Philip W
authors.initials: PW
authors.lastname: Davidson
authors.forename: Christopher
authors.initials: C
authors.lastname: Cox
authors.forename: Fenyuan
authors.initials: F
authors.lastname: Xiao
authors.forename: Sally W
authors.initials: SW
authors.lastname: Thurston
authors.forename: Elsa
authors.initials: E
authors.lastname: Cernichiari
authors.forename: Conrad F
authors.initials: CF
authors.lastname: Shamlaye
authors.forename: Jean
authors.initials: J
authors.lastname: Sloane-Reeves
authors.forename: Lesley
authors.initials: L
authors.lastname: Georger
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Clarkson
mesh_terms: D002648:Child; D002657:Child Development / Q000187:drug effects*; D002675:Child, Preschool; D016000:Cluster Analysis; D015331:Cohort Studies; D004305:Dose-Response Relationship, Drug; D005260:Female; D005500:Follow-Up Studies; D005506:Food Contamination; D006801:Humans; D007223:Infant; D007360:Intelligence; D007361:Intelligence Tests; D008767:Methylmercury Compounds / Q000009:adverse effects*; D015233:Models, Statistical; D009043:Motor Activity / Q000187:drug effects*; D009483:Neuropsychological Tests; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D012044:Regression Analysis; D017747:Seafood; D012750:Seychelles; D012931:Social Environment; D012959:Socioeconomic Factors; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000009:adverse effects*
chemical_list: D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical