A tale of two PG systems: A comparison of the two most widely used continuous probabilistic genotyping systems in the United States

IF 1.5 4区 医学 Q2 MEDICINE, LEGAL Journal of forensic sciences Pub Date : 2024-06-20 DOI:10.1111/1556-4029.15571
Susan A. Greenspoon PhD, Lisa Schiermeier-Wood MS, Bradford C. Jenkins MS
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Abstract

The development of probabilistic genotyping (PG) systems to quantitatively analyze DNA mixture samples has been transformative in forensic science. TrueAllele® Casework (TA) and STRmix™ (STRmix) are the two most widely used PG systems in the United States. The two systems were challenged with 48 two-, three-, and four-person mock casework samples, for a total of 152 likelihood ratio (LR) comparisons. TA and STRmix converged on the same result (supportive, non-supportive, or inconclusive) for ~91% of contributor-specific comparisons. Where moderate or substantial differences in log(LR) values were observed, 9% affected the conclusion of the reference association to the mixture. The PG systems exhibited high correlations for estimated contributor-specific template quantities (~92%) and log(LR)s produced (>88%). When the log(LR)s for only low-template contributors (<100 pg) were compared, the R2 value dropped to ~68% and the difference became statistically significant. Of the 14 contributor comparisons where the conclusion differed, two were contradictory (supportive vs. non-supportive) and 12 were either inconclusive versus non-supportive or inconclusive versus supportive. The differing results were likely due to dissimilarities in the mixture input file as STRmix uses a lab-defined analytical threshold (AT) and TA models to 10 RFUs for each electropherogram. When 7 of the 14 mixtures were reanalyzed by STRmix using a 10 RFU AT, the log(LR)s for the low-template contributors became more similar to TAs. This study shows that while both systems may produce accurate and calibrated LRs, their results can deviate, especially for low-template, degraded contributors, and the deviation is generally predictable.

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两个 PG 系统的故事:美国最广泛使用的两种连续概率基因分型系统的比较。
用于定量分析 DNA 混合样本的概率基因分型 (PG) 系统的开发在法医学领域产生了变革性的影响。TrueAllele® Casework (TA) 和 STRmix™ (STRmix) 是美国使用最广泛的两种 PG 系统。这两个系统分别使用了 48 个两人、三人和四人模拟案件样本,共进行了 152 次似然比 (LR) 比较。在约 91% 的特定贡献者比较中,TA 和 STRmix 得出了相同的结果(支持、不支持或不确定)。在观察到对数(LR)值存在中度或重大差异的情况下,9%的差异影响了混合物的参考关联结论。PG 系统对估计的特定贡献者模板数量(约 92%)和产生的 log(LR)s 显示出较高的相关性(>88%)。当只有低模板贡献者的对数(LR)(2 值降至约 68%,差异变得具有统计学意义。在 14 个结论不同的贡献者比较中,有两个是矛盾的(支持与不支持),12 个是不确定与不支持或不确定与支持。不同的结果很可能是由于混合物输入文件中的差异造成的,因为 STRmix 使用实验室定义的分析阈值(AT)和 TA 模型,每个电图的分析阈值为 10 个 RFU。当 STRmix 使用 10 RFU AT 对 14 种混合物中的 7 种进行重新分析时,低模板贡献者的 log(LR)s 变得与 TA 更为相似。这项研究表明,虽然这两种系统都能产生准确的校准 LRs,但它们的结果可能会出现偏差,特别是对于低模板、降解的贡献物,而且偏差一般是可以预测的。
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来源期刊
Journal of forensic sciences
Journal of forensic sciences 医学-医学:法
CiteScore
4.00
自引率
12.50%
发文量
215
审稿时长
2 months
期刊介绍: The Journal of Forensic Sciences (JFS) is the official publication of the American Academy of Forensic Sciences (AAFS). It is devoted to the publication of original investigations, observations, scholarly inquiries and reviews in various branches of the forensic sciences. These include anthropology, criminalistics, digital and multimedia sciences, engineering and applied sciences, pathology/biology, psychiatry and behavioral science, jurisprudence, odontology, questioned documents, and toxicology. Similar submissions dealing with forensic aspects of other sciences and the social sciences are also accepted, as are submissions dealing with scientifically sound emerging science disciplines. The content and/or views expressed in the JFS are not necessarily those of the AAFS, the JFS Editorial Board, the organizations with which authors are affiliated, or the publisher of JFS. All manuscript submissions are double-blind peer-reviewed.
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