Review A Retrospective Performance Assessment of the Developmental Neurotoxicity Study in Support of OECD Test Guideline 426 Susan L. Makris,1 Kathleen Raffaele,2 Sandra Allen,3 Wayne J. Bowers,4 Ulla Hass,5 Enrico Alleva,6 Gemma Calamandrei,6 Larry Sheets,7 Patric Amcoff,8 Nathalie Delrue,8 and Kevin M. Crofton9 1Office of Research and Development, National Center for Environmental Assessment, and 2Office of Pesticide Programs, U.S. Environmental Protection Agency, Washington, DC, USA; 3Syngenta CTL, Cheshire, UK; 4Environmental Health Science Bureau, Health Canada, Ottawa, Canada; 5Department of Toxicology and Risk Assessment, National Food Institute, Technical University of Denmark, Søborg, Denmark; 6Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Rome, Italy; 7Bayer CropScience LP, Stilwell, Kansas, USA; 8Environment, Health, and Safety Division, Organisation of Economic Co-operation and Development, Paris, France; 9Office of Research and Development, National Health and Environmental Effects Research Laboratories, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA Objectiv : We conducted a review of the history and performance of developmental neurotoxicity (DNT) testing in support of the finalization and implementation of Organisation of Economic Co-operation and Development (OECD) DNT test guideline 426 (TG 426). i nf : In this review we summarize extensive scientific efforts that Ormati On s Ources nad nalysi form the foundation for this testing paradigm, including basic neurotoxicology research, interlabo- ratory collaborative studies, expert workshops, and validation studies, and we address the relevance, applicability, and use of the DNT study in risk assessment. c Onclusi Ons : The OECD DNT guideline represents the best available science for assessing the potential for DNT in human health risk assessment, and data generated with this protocol are rele- vant and reliable for the assessment of these end points. The test methods used have been subjected to an extensive history of international validation, peer review, and evaluation, which is contained in the public record. The reproducibility, reliability, and sensitivity of these methods have been demonstrated, using a wide variety of test substances, in accordance with OECD guidance on the validation and international acceptance of new or updated test methods for hazard characteriza- tion. Multiple independent, expert scientific peer reviews affirm these conclusions. Key w Ords : children’s health, developmental neurotoxicity, guideline, hazard assessment, Organisation of Economic Co-operation and Development, risk assessment, U.S. Environmental Protection Agency. Environ Health Perspect 117:17–25 (2009). doi:10.1289/ehp.11447 available via http://dx.doi.org/ [Online 12 August 2008] The purpose and intent of this retrospective per- formance assessment was to review the history of developmental neurotoxicity (DNT) testing. This review demonstrates the extensive scientific efforts, including basic neurotoxicology research, interlaboratory collaborative studies, expert workshops, and validation studies, that form the foundation for this testing paradigm. We also review the relevance, applicability, and use of the DNT study in human health risk assessment and the historical performance of the DNT study. This analysis was developed by an OECD expert group [Organisation for Economic Co-operation and Development (OECD) 2008a] in support of drafting the OECD DNT Test Guideline 426 (TG 426; OECD 2007) that satisfies cur- rent OECD validation criteria. OECD validation criteria are described in Guidance Document 34 (GD34; OECD 2005a), which addresses the validation and regulatory acceptance of new or updated test methods for hazard characterization. They are based on the “Solna Principles” for validation and regulatory acceptance (OECD 1996b), but additionally emphasize the importance of flexibility and adaptability in the validation process without compromising scientific rigor. GD34 (OECD 2005a) also provides concise definitions of related concepts such as accuracy, concordance, performance standards, predictivity, relevance, reliability, repeatabil- ity, reproducibility, sensitivity, and specificity. The terminology and definitions presented in GD34 (Annex 1) were used in the DNT review process; however, individual studies may have varied slightly in the definition of terms. The first DNT guideline was devel- oped by the U.S. Environmental Protection Agency (EPA) and has been subjected to numerous validation studies and rigorous peer reviews over the years. The U.S. EPA has deemed the method validated for its regula- tory purposes. As described herein, extensive supportive materials for the relevance, reli- ability, and overall performance of the DNT study are available. Until recently, only the U.S. EPA DNT guideline has been avail- able for testing laboratories. The new OECD TG 426 (OECD 2007) DNT guideline will fill a regulatory gap for OECD member countries. This review summarizes the con- siderable work that has been performed in the development of the DNT study and provides the rationale for the regulatory acceptance of TG 426 as a new OECD test guideline. The U.S. EPA DNT guideline (U.S. EPA 1998), the prototype for TG 426, was founded upon an extensive scientific data- base. This includes interlaboratory validation studies, such as the Collaborative Behavioral Environmental Health Perspectives • volume 117 | number 1 | January 2009 Teratology Study (CBTS), which was con- ducted in the mid-1980s. A separate group of experts at the Williamsburg Workshop (Kimmel et al. 1990) agreed that the meth- ods in the DNT study are sensitive to known human developmental neurotoxicants. An expert consultation meeting conducted in 2000 (OECD 2003) discussed issues on vali- dation, especially of individual test compo- nents versus the whole DNT test method. In doing so, they reviewed the extensive history of international validation, peer review, and evaluation of DNT methods contained in the public record. Experts agreed that individual assays of the DNT test method have been shown to be relevant, reliable, and sensitive and that extensive information demonstrates the validity of individual components of the DNT test method (OECD 2003). The field of developmental neuro- toxicology evolved from the disciplines of neurotoxicology, experimental and develop- ment psychology, and developmental toxicology, through an extensive history of sci- entific research and regulatory consideration. Developmental toxicity is defined in GD43 (OECD 2008b), which states that effects may result from either prenatal or postnatal expo- sure, may manifest at any life stage, and may be expressed as functional deficits. The DNT study is a specialized type of developmental toxicity study designed to screen for adverse effects of pre- and postnatal exposure on the development and function of the nervous system and to provide dose– response characterizations of those outcomes. The U.S. EPA and OECD DNT guidelines recommend administration of the test sub- stance during gestation and lactation. Cohorts of offspring (typically rat) are randomly W a s h i n g t o n , D C Address correspondence to S. Makris, U.S. EPA, ORD, NCEA, Mail code: 8623P, 1200 Pennsylvania A v e . N W , 2 0 4 6 0 - 0 0 0 1 . Telephone: (703) 347-8522. Fax: (703) 347-8592. E-mail: makris.susan@epa.gov The views expressed in this document are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency. The authors declare they have no competing financial interests. Received 5 March 2008; accepted 12 August 2008. 17