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ARTICLES: Martha M. Téllez-Rojo, David C. Bellinger, Carmen Arroyo-Quiroz, Héctor Lamadrid-Figueroa, Adriana Mercado-García, Lourdes Schnaas-Arrieta, Robert O. Wright, Mauricio Hernández-Avila, and Howard Hu Longitudinal Associations Between Blood Lead Concentrations Lower Than 10 µg/dL and Neurobehavioral Development in Environmentally Exposed Children in Mexico City Pediatrics 2006; 118: e323-e330 [Abstract] [Full text] [PDF]

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Apparent contradiction to the authors' study published in 2002

joseph scheller   (9 August 2006)

Response: Apparent contradiction to the authors' study published in 2002

Martha M Téllez-Rojo, David C. Bellinger, Carmen Arroyo-Quiroz, Héctor Lamadrid-Figueroa, Adriana Mercado-García, Lourdes Schnaas-Arrieta, Robert O. Wright, Mauricio Hernández-Avila, and Howard Hu   (18 September 2006)

Apparent contradiction to the authors' study published in 2002 9 August 2006
joseph scheller, physician children's national medical center Send letter to journal: Re: Apparent contradiction to the authors' study published in 2002 jschelle{at}cnmc.org joseph scheller	In this study Dr Tellez-Rojo et al conclude that blood levels of lead at 24 months were inversely related to MDI and PDI at 24 months. Umbilical cord blood lead did not alter this relationship. The authors do not cite their previous work published in Pediatrics 2002 titled 'Maternal Bone Lead as an Indepent Risk Factor for Fetal Neurotoxicity'. This previous study seems to have used data from the same patient population, but concludes that 'lead levels in umbilical cord and trabecular bone were significantly and independently inversely associated with MDI scores at 24 months'. I'd like the authors to explain this apparent contradiction, and to explain why they did not cite this study in the current publication. joseph scheller md child neurology children's national medical center washington dc Conflict of Interest: i have served as an expert witness in lead paint litigation.
Response: Apparent contradiction to the authors' study published in 2002 18 September 2006
Martha M Téllez-Rojo, Researcher National Institute of Public Health, Mexico, David C. Bellinger, Carmen Arroyo-Quiroz, Héctor Lamadrid-Figueroa, Adriana Mercado-García, Lourdes Schnaas-Arrieta, Robert O. Wright, Mauricio Hernández-Avila, and Howard Hu Send letter to journal: Re: Response: Apparent contradiction to the authors' study published in 2002 mmtellez{at}insp.mx Martha M Téllez-Rojo, et al.	We appreciate Dr. Scheller's letter and apologize for any confusion we may have inadvertently caused by not citing the previous study. There are several reasons why the 2 studies differ and we believe direct comparison is not appropriate. The differing results are likely due to the following: 1. The study populations are not the same. Our 2006 paper’s analyses was conducted on two birth cohorts, one of them was indeed analyzed for the 2002 paper while the other was not. To be precise, only 71 (24%) of the children analyzed for the 2006 study were also analyzed for the 2002 study. 2. Because lead was phased out from gasoline in 1997, the second cohort had overall lower blood lead levels, including lower umbilical cord lead levels, and therefore greater representation in the final analysis. Our 2006 analysis was restricted only to children with low blood Pb levels (measurements were always below 10 ug/dL). This restriction did not operate in the 2002 analyses, and thus, the populations are not strictly comparable as both cord and concurrent blood Pb levels are much lower in our current study. As stated above, the children from the 2nd cohort were not included in the 2002 paper. 3. In addition to differences in the overall "lead exposure dose" in the 2 studies, both studies had different objectives. The 2002 study was aimed at assessing the effect of Prenatal Pb exposure as reflected both on maternal Pb burden and newborn blood Pb concentrations. Its main conclusion was that maternal bone Pb is related to neurobehavioral development regardless of the blood Pb concentration in the newborn, which suggests that mobilization of bone lead stores during early stages of pregnancy is responsible. On the other hand, the objective of our 2006 study was to determine if continuous postnatal Pb exposure to low (below 10 ug/dL) blood Pb levels during early life had consequences on children’s neurobehavior, independently of prenatal exposure. We apologize for not citing the prior publication but considering these fundamental differences we did not consider citing the previous study as necessary. Conflict of Interest: None declared