Peters Kelsey C, Swaminathan Harish, Sheehan Jennifer, Duffy Ken R, Lun Desmond S, Grgicak Catherine M
Biomedical Forensic Sciences, Boston University School of Medicine, United States.
Hamilton Institute, Maynooth University, Ireland.
Forensic Sci Int Genet. 2017 Nov;31:160-170. doi: 10.1016/j.fsigen.2017.09.005. Epub 2017 Sep 8.
Samples containing low-copy numbers of DNA are routinely encountered in casework. The signal acquired from these sample types can be difficult to interpret as they do not always contain all of the genotypic information from each contributor, where the loss of genetic information is associated with sampling and detection effects. The present work focuses on developing a validation scheme to aid in mitigating the effects of the latter. We establish a scheme designed to simultaneously improve signal resolution and detection rates without costly large-scale experimental validation studies by applying a combined simulation and experimental based approach. Specifically, we parameterize an in silico DNA pipeline with experimental data acquired from the laboratory and use this to evaluate multifarious scenarios in a cost-effective manner. Metrics such as signal-to-noise resolution, false positive and false negative signal detection rates are used to select tenable laboratory parameters that result in high-fidelity signal in the single-copy regime. We demonstrate that the metrics acquired from simulation are consistent with experimental data obtained from two capillary electrophoresis platforms and various injection parameters. Once good resolution is obtained, analytical thresholds can be determined using detection error tradeoff analysis, if necessary. Decreasing the limit of detection of the forensic process to one copy of DNA is a powerful mechanism by which to increase the information content on minor components of a mixture, which is particularly important for probabilistic system inference. If the forensic pipeline is engineered such that high-fidelity electropherogram signal is obtained, then the likelihood ratio (LR) of a true contributor increases and the probability that the LR of a randomly chosen person is greater than one decreases. This is, potentially, the first step towards standardization of the analytical pipeline across operational laboratories.
在实际案件工作中，经常会遇到含有低拷贝数DNA的样本。从这些样本类型中获取的信号可能难以解释，因为它们并不总是包含每个贡献者的所有基因型信息，其中遗传信息的丢失与采样和检测效应有关。目前的工作重点是开发一种验证方案，以帮助减轻后者的影响。我们建立了一种方案，通过应用基于模拟和实验相结合的方法，在不进行昂贵的大规模实验验证研究的情况下，同时提高信号分辨率和检测率。具体来说，我们利用从实验室获取的实验数据对计算机模拟DNA流程进行参数化，并以此以经济高效的方式评估各种情况。诸如信噪比分辨率、假阳性和假阴性信号检测率等指标用于选择在单拷贝状态下能产生高保真信号的可行实验室参数。我们证明，从模拟中获得的指标与从两个毛细管电泳平台和各种进样参数获得的实验数据一致。一旦获得良好的分辨率，如有必要，可使用检测误差权衡分析来确定分析阈值。将法医鉴定过程的检测限降低到一份DNA拷贝是增加混合物中微量成分信息含量的有力机制，这对于概率系统推断尤为重要。如果法医鉴定流程经过精心设计，能够获得高保真的电泳图谱信号，那么真实贡献者的似然比（LR）就会增加，而随机选择的人的LR大于1的概率就会降低。这可能是朝着跨运营实验室的分析流程标准化迈出的第一步。
