To the best of our knowledge, this is the first systematic review that evaluates the relationships of genetic variants and plasma level of TGF-b 1 with risk of PE. However, this study has some limitations. First, the number of studies included in the metaanalysis is comparably small and could not avoid publication bias. Although the genetic variants in PE have been investigated by hundreds of studies, MSAB TGF-b 1 is not a popular candidate gene since only five studies were identified after literature search. This is partly because TGF-b 1 was firstly identified as a candidate gene of PE as late as in 2007 and its possible role in the pathogenesis of PE was described only recently. Compared with other widely studied candidate genes, the TGF-b 1 gene is a younger and lessstudied one. Although the results of our meta-analysis suggest that TGF-b 1 869 T.C polymorphism was associated with risk of PE, this result was mainly determined by the study of Kim et al. and Aguilar-Duran et al.. Therefore, further studies are needed. Second,EB1089 it is unsuitable to conduct a meta-analysis because of significant heterogeneity among studies on plasma TGF-b 1 level and PE risk. The substantial heterogeneity is probably due to the complexity of measuring methodology of TGF-b 1 level and this can also be an obstacle for further application of TGF-b 1 as a clinical indicator. However, studies show significant differences in TGF-b 1 plasma levels between PE patients and normal pregnant women, indicating that TGF-b 1 may play a role in the pathogenesis of PE. Nevertheless, this issue should be investigated by further studies. Respiration is a fundamental process in all living organisms, whether aerobic or anaerobic. The basic process of respiration involves three major steps which include: donation of electrons by a low-redox potential electron donor, electron transfer via a range of membrane-associated redox cofactors or complexes, and the reduction of a high redox potential electron acceptor, thereby terminating the process. This ‘‘electron transfer’’ or respiratory chain is situated inside the mitochondrial membrane or cell membrane of eukaryotes and prokaryotes, respectively.