Bonsu Dan Nana Osei, Mitchell Natasha, Jeanes Claire, Henry Julianne
Chemistry and Forensic Science, Griffith Sciences, Griffith University, Nathan, Queensland, Australia.
Faculty of Science Technology and Engineering, School of Biological Sciences, The University of Adelaide, Adelaide, South Australia, Australia.
J Forensic Sci. 2025 May;70(3):1133-1148. doi: 10.1111/1556-4029.70027. Epub 2025 Mar 21.
Following an alleged sexual assault, a victim may undergo a medical examination whereby internal or external bodily swabs may be collected and submitted to a forensic laboratory to be screened for the presence of semen. At Forensic Science SA (FSSA), this involves microscopic examination of a smear prepared from each swab for the presence of sperm. Microscopic detection of sperm is confirmatory for semen, but the process is very time-consuming, especially where very low levels are present. Moreover, microscopy results are not a reliable predictor of the amount of male DNA that might be recovered. SWGDAM recommends a direct-to-DNA approach as an efficient alternative. Therefore, we investigated the Qiagen Casework GO! kit (CWG), in conjunction with the Y-chromosome marker in the Quantifiler Trio DNA quantification kit, for the rapid screening of sexual assault swabs for the presence of male DNA (termed 'Y-screen'). We initially investigated two swab types, the Copan cotton swab (currently used in Forensic Examination Collection Kits (FECK) submitted to FSSA) and the Sarstedt Forensic XL swab (a Forensic DNA grade alternative). The optimal size of the swab cutting and the volume of CWG lysis mix for the Y-screen was determined to be 1/8 and 100 μL, respectively, which ensured cost minimization and sample preservation. The performance of the optimized Y-screen method was compared with conventional microscopy using a series of simulated sexual assault swabs constructed by spiking female buccal swabs with serial dilutions of semen. For Copan cotton swabs, all samples with detectable sperm by microscopy had detectable levels of male DNA using the Y-screen. The Y-screen also showed greater sensitivity than microscopy for this swab type, detecting male DNA in 8% of samples where sperm was not observed. In contrast, 36% of Forensic XL swabs gave undetectable male DNA when sperm was observed by microscopy, which indicated that the Y-screen approach with CWG may not be compatible with all swab types. A casework trial of the Y-screen approach using 46 FECK swabs (Copan cotton swabs) submitted across 29 cases confirmed the higher sensitivity of the Y-screen approach as compared to conventional microscopy. Here, 44% of FECK swabs that had no observable sperm by microscopy had detectable male DNA using the Y-screen. There were no instances where the FECK swabs with observable sperm by microscopy had undetectable male DNA using the Y-screen. Our study confirmed the utility of the Y-screen approach using CWG to expedite the downstream DNA analysis of FECK swab samples in operational casework.
在被指控遭受性侵犯后，受害者可能会接受医学检查，在此过程中可能会采集体内或体外的身体拭子，并将其提交给法医实验室，以筛查精液的存在。在南澳大利亚法医科学局（FSSA），这涉及对从每个拭子制备的涂片进行显微镜检查，以查找精子的存在。通过显微镜检测到精子可确认精液的存在，但该过程非常耗时，尤其是在精子含量极低的情况下。此外，显微镜检查结果并不能可靠地预测可能回收的男性DNA的量。西南法医DNA分析方法工作组（SWGDAM）推荐采用直接进行DNA检测的方法作为一种有效的替代方法。因此，我们研究了Qiagen Casework GO!试剂盒（CWG），并结合Quantifiler Trio DNA定量试剂盒中的Y染色体标记，用于快速筛查性侵犯拭子中男性DNA的存在（称为“Y筛查”）。我们最初研究了两种拭子类型，Copan棉拭子（目前用于提交给FSSA的法医检查采集试剂盒（FECK）中）和Sarstedt法医XL拭子（一种法医DNA级别的替代品）。确定用于Y筛查的拭子切割最佳尺寸和CWG裂解混合物体积分别为1/8和100μL，这确保了成本最小化和样品保存。使用一系列通过用连续稀释的精液加样到女性口腔拭子上构建的模拟性侵犯拭子，将优化后的Y筛查方法的性能与传统显微镜检查进行了比较。对于Copan棉拭子，通过显微镜检测到有精子的所有样品，使用Y筛查均检测到了可检测水平的男性DNA。对于这种拭子类型，Y筛查还显示出比显微镜检查更高的灵敏度，在8%未观察到精子的样品中检测到了男性DNA。相比之下，当通过显微镜观察到有精子时，36%的法医XL拭子未检测到男性DNA，这表明使用CWG的Y筛查方法可能与所有拭子类型不兼容。使用来自29个案件提交的46个FECK拭子（Copan棉拭子）对Y筛查方法进行的实际案件试验证实，与传统显微镜检查相比，Y筛查方法具有更高的灵敏度。在此，44%通过显微镜未观察到精子的FECK拭子，使用Y筛查检测到了可检测的男性DNA。没有出现通过显微镜观察到有精子的FECK拭子，使用Y筛查却未检测到男性DNA的情况。我们的研究证实了使用CWG的Y筛查方法在实际案件工作中加快FECK拭子样品下游DNA分析的实用性。
