Objective      To screen serum biomarkers of Down’s syndrome (DS) in the maternal serum and evaluate their values in clinical practice.      Methods       Maternal serum samples from 6 pregnant women who were confirmed to be carrying DS fetuses (DS group) and 6 normal pregnant women with non-DS pregnancies (control group) in the second-trimester were collected in our prenatal diagnostic center. The samples were analyzed by 2-dimensional gel electrophoresis (2-DE) to screen the proteins with different expression for potential predictive biomarkers of DS-affected pregnancies. Then the serum proteins expressed most differentially in DS group were identified by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Differential levels of complement factor H-related protein 1 (CFHR1) and kininogen 1 were further verified by Western blotting.      Results       The analysis of 2-DE results revealed 29 protein spots having significantly differed expression levels between DS and control groups. Then several differentially expressed proteins

including CFHR1 and kininogen 1

were successfully identified by MALDI-TOF-MS. Western blotting indicated the integrated density values of CFHR1 and kininogen 1 were 5 687.0±727.8 and 133 451.8±32 118.8 respectively in DS group

significantly higher than those in control group (1 414.1±715.6

P0.01

33 073.9±14 390.4

P0.05).      Conclusion       2-DE and mass spectrometry analysis is a reliable method for screening protein markers. Western blotting confirms that the differential expression of CFHR1 and kininogen 1 are involved in DS-affected pregnancies

and might serve as potential predictive biomarkers for prenatal screening.