PLoS Medicine | www.plosmedicine.org 1129 Correspondence June 2007 | Volume 4 | Issue 6 | e211 | e225 Reporting of Systematic Reviews: The Challenge of Genetic Association Studies Muin J. Khoury, Julian Little, Julian Higgins, John P. A. Ioannidis, Marta Gwinn We applaud PLoS editors for their commitment to publishing high-quality systematic reviews (SRs) [1]. Moher et al. [2] clearly documented the inconsistent quality of reporting of SRs. With more than 2,500 SRs published every year, low-quality or outdated reviews may mislead researchers, providers, and policy makers. The situation could be improved if more evidence-based reporting guidelines were agreed upon, developed, and adhered to. The growing fi eld of genetic associations (GAs) illustrates the urgent need for transparent SRs and meta-analyses. Already, thousands of articles on GAs have been published, and the application of high-throughput genotyping methods may exponentially increase the number of reported associations [3]. Selective reporting of large numbers of false- positive associations could undermine the fi eld and interfere with our ability to translate advances in genomics into clinical practice. To address these problems, the Human Genome Epidemiology Network (HuGENet) was started as a global collaboration to strengthen methods of analysis and reporting of GAs and to develop a reliable knowledge base on the association between genetic variation and human diseases [4]. Between 2001 and 2006, the HuGENet online database assembled more than 25,000 published articles on GAs and more than 500 systematic reviews of GAs. Nevertheless, there are large inconsistencies in the quality of genetic association studies [5] and in the reporting of SRs of such associations [6]. In collaboration with several journals, HuGENet promotes the publication of transparently reported SRs of gene���disease associations [4]. More than 50 HuGE reviews have been published over the past six years. After several HuGENet workshops bringing together researchers from different fi elds and journal editors, the fi rst edition of a HuGENet handbook, modeled in part after the Cochrane handbook of systematic reviews, was published on the Canadian HuGENet Web site [7]. The handbook describes methodological issues and outlines steps in conducting such reviews, including the need for a detailed protocol. It also discusses meta-analysis methods. We strongly encourage researchers interested in conducting systematic reviews of GAs to consult the HuGENet handbook, and adopt transparent protocols. Retrospective SRs of published data have limitations, even when properly conducted. Investigators can advance the fi eld of human genome epidemiology by conducting prospective meta-analyses and large collaborative analyses through international consortia. HuGENet has created a Network of Investigator Networks to help the growth of such initiatives [8]. Muin J. Khoury (muk1@cdc.gov) Marta Gwinn Centers for Disease Control and Prevention Atlanta, Georgia, United States of America Julian Little University of Ottawa Ottawa, Ontario, Canada Julian Higgins Institute of Public Health Cambridge, United Kingdom John P. A. Ioannidis University of Ioannina School of Medicine Ioannina, Greece References 1. The PLoS Medicine Editors (2007) Many reviews are systematic but some are more transparent and completely reported than others. PLoS Med 4: e147. doi:10.1371/journal.pmed.0040147 2. Moher D, Tetzlaff J, Tricco AC, Sampson M, Altman DG (2007) Epidemiology and reporting characteristics of systematic reviews. PLoS Med 4: e78. doi: 10.1371/journal.pmed.0040078 3. Khoury MJ, Little J, Gwinn M, Ioannidis JP (2006) On the synthesis and interpretation of consistent but weak gene-disease associations in the era of genome-wide association studies. Int J Epidemiol. E-pub 20 December 2006. 4. Centers for Disease Control and Prevention (2007) Human Genome Epidemiology Network (HuGENet). Available: http://www.cdc.gov/ genomics/hugenet/default.htm. Accessed 24 May 2007. 5. Bogardus ST Jr, Concato J, Feinstein AR (1999) Clinical epidemiological quality in molecular genetic research: The need for methodological standards. JAMA 281: 1919���1926. 6. Attia J, Thakkinstian A, D���Este C (2003) Meta analysis of molecular association studies: Methodologic lessons for genetic epidemiology. J Clin Epidemiol 56: 297���303. 7. Little J, Higgins J, editors (2006) The HuGENet HuGE review handbook, version 1.0. Available: http://www.genesens.net/_intranet/doc_nouvelles/ HuGE%20Review%20Handbook%20v11.pdf. Accessed 24 May 2007. 8. Ioannidis JP, Gwinn M, Little J, Higgins JP, Bernstein JL, et al. (2006) A road map for effi cient and reliable human genome epidemiology. Nat Genet 38: 3���5. Citation: Khoury MJ, Little J, Higgins J, Ioannidis JPA, Gwinn M (2007) Reporting of Systematic Reviews: The challenge of genetic association studies. PLoS Med 4(6): e211. doi:10.1371/journal.pmed.0040211 Copyright: This is an open-access article distributed under the terms of the Creative Commons Public Domain Declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modifi ed, built upon, or otherwise used by anyone for any lawful purpose. Funding: The authors received no specifi c funding for this article. Competing Interests: The authors have declared that no competing interests exist. Reporting of Systematic Reviews: Better Software Required Jan Brogger This is an important paper and editorial [1,2]. Systematic reviews should be much more widespread, and not only for randomized clinical trials of clinical treatments. A paper on an elegant piece of experimental data or on epidemiological observations would be made all the more interesting if the fi rst table were a high-quality assessment of previous studies. In fact, I would suggest that performing a systematic review should be part of a research protocol for any subject, even before the study is initiated. However, this paper confi rms my suspicion that the rising popularity of ���systematic reviews��� has not been followed by adherence to methodological rigor. With this background, I would like to point out one weakness that may explain part of the current quality defi cit in some systematic reviews. There is a substantial lack of software that can assist in an important part of a systematic review: tracking literature searches and early phase screening. From

PLoS Medicine | www.plosmedicine.org 1130 browsing of the literature and communications with various Norwegian and Danish Cochrane collaborators (including the RevMan developers), there seems to be a limited number of tools for this use. Oftentimes, it is suggested that commercial reference management software be used, such as the popular EndNote. These types of software were not designed with systematic reviews in mind. At later stages of a review, Cochrane���s RevMan is useful, but not early on. As far as I have been able to ascertain, there are only two tools presently available. The fi rst is EPPI-Reviewer (http:������eppi.ioe.ac.uk/cms/Default.aspx?tabid=184), which is non-profi t, but does not seem to be open source or available for local deployment. The second is TrialStat���s SRS software (http://www.trialstat.com), which is commercial and has a substantial price tag. I would therefore encourage researchers and institutions to contribute to the development of open-source tools for assisting in systematic reviews. I am currently writing such a simple tool, based on the open-source JabRef package (http://sourceforge.net/projects/jabref) and would welcome feedback on perceived needs and other similar projects. Jan Brogger (jan.brogger@nevro.uib.no) University of Bergen Bergen, Norway References 1. Moher D, Tetzlaff J, Tricco AC, Sampson M, Altman DG (2007) Epidemiology and reporting characteristics of systematic reviews. PLoS Med 4: e78. doi: 10.1371/journal.pmed.0040078 2. The PLoS Medicine Editors (2007) Many reviews are systematic but some are more transparent and completely reported than others. PLoS Med 4: e147. doi:10.1371/journal.pmed.0040147 Citation: Brogger J (2007) Reporting of Systematic Reviews: Better software required. PLoS Med 4(6): e225. doi:10.1371/journal.pmed.0040225 Copyright: �� 2007 Jan Brogger. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The author received no specifi c funding for this article. Competing Interests: The author has declared that no competing interests exist. Neuraminidase Antibodies and H5N1: Geographic-Dependent Infl uenza Epidemiology Could Determine Cross- Protection against Emerging Strains Jesus F. Bermejo-Martin, David J. Kelvin, Yi Guan, Honglin Chen, Pilar Perez-Bre��a, Inmaculada Casas, Eduardo Arranz, Raul O. de Lejarazu We have read with great interest the work of Sandbulte et al. recently published in your journal [1]. In this article, the authors provide evidence for the existence of cross-immunity between the neuraminidase of H5N1 viruses and that of endemic human H1N1 viruses. Age may be an important determining factor in the development of cross-immunity: younger people, having a shorter history of H1N1 exposure, may be disproportionately susceptible to H5N1 infection. We would like to highlight the infl uence of the geographic- dependent epidemiological behaviour of infl uenza in the development of cross-immunity. While Europe, the United States, and northern Asia experience regular outbreaks of infl uenza each year, (���seasonal infl uenza���), infl uenza in tropical regions such as southern China, Vietnam, and Indonesia tends to be year-round (���non-seasonal��� infl uenza). In consequence, the probability of exposure to infl uenza A in these regions persists throughout the entire year. Repetitive contacts with infl uenza wild viruses could promote the development of cross-immunity against different viral strains. Even more, it could represent a fortuitous mechanism for developed natural protection by the close and persistent exposure of the immune system to infl uenza wild viruses in regions known for being an important source of emergent viruses, like southern China. Results from Sandbulte et al. show that antibodies play a dominant role in cross-protection. The authors underscore the possible benefi t of seasonal infl uenza vaccination for human populations faced with the threat of pandemic H5N1 infl uenza. This idea deserves careful analysis. The main group at risk for severe complications of seasonal fl u are people older than 65. In Western countries, this population is recommended to receive annual vaccinations. Generally speaking, elder vaccination rates in tropical countries are far lower than those in Western countries. Even with the low annual vaccination rate in elders, H5N1 infection is observed mostly in young people. The existence of sub-clinical or asymptomatic infections in elderly people cannot be ruled out, but the reason why there are no described clinical cases of H5N1 in people older than 40 years is currently unknown. An age-dependent differential distribution of avian-type receptors in the upper respiratory tract could be a possible explanation. On the other hand, Tumpey et al. [2] demonstrated that mucosal (but not parenteral) challenges with inactivated or live H3N2 virus protect against H5N1 infection in mice. These results could have a relevant consequence: does contact with circulating infl uenza A via the respiratory tract confer a higher degree of cross- protection than parenteral exposure to vaccines? In conclusion, the non-seasonal epidemiological behaviour of infl uenza in tropical countries could dramatically infl uence the development of naturally induced cross-immunity against different infl uenza strains and diminish the risk of severe disease from new emergent strains in elderly people living in these countries. The apparent lack of H5N1 cases in the elderly may be the result of continued exposure to circulating non-seasonal infl uenza A via mucosal epithelium in the respiratory tract. Vaccination via the mucosal route could be a more effi cient way to provide cross-protection against future pandemic strains than vaccination via the parenteral route. In this hypothetical scenario, Western countries would be under- protected. Jesus F. Bermejo-Martin (bermejo@ped.uva.es) Eduardo Arranz Raul O. de Lejarazu University of Valladolid Valladolid, Spain David J. Kelvin Joint Infl uenza Research Center, Division of Immunology Shantou University Medical College Shantou, People���s Republic of China Division of Experimental Therapeutics Toronto General Research Institute, University Health Network Toronto, Ontario, Canada June 2007 | Volume 4 | Issue 6 | e225 | e212