Weight-of-evidence for DNA identification of missing persons and human remains using CODIS.

DNA Identification of unidentified human remains (UHR) is performed in Israel by comparing the UHR's short tandem repeat (STR) profiles to a national database of STR profiles taken from relatives of missing persons. Kinship analysis is performed using the CODIS 7.0 software and results are stated as a Joint Pedigree Likelihood Ratio (JPLR). The weight-of-evidence for JPLR has never been studied, making it difficult to interpret the meaning of specific values in terms of whether UHR are related to specific pedigrees. Therefore, the aim of this study was to statistically determine the practical meaning and context of the JPLR. We used 440 million pairs of simulated DNA profiles and 294 pairs of real ones from known siblings, parent/offspring and unrelated persons. A Score-Based Likelihood Ratio (SBLR) was empirically constructed, validated and compared to both JPLR and the LR produced by CODIS. Our results show that CODIS's JPLR and LR values for single-person pedigrees overestimate the level of support for both "parent/child" and "siblings" propositions relative to the "unrelated" proposition, by up to two orders of magnitude. A practical table is given for correcting this phenomenon, with statistical interpretation (i.e. SBLR) for each JPLR score, including verbal levels of propositional support ranging from "no support" (SBLR<2) to "extremely strong" (SBLR>1 Million).

A new search tool for familial searches in the Israel Criminal DNA database.

The Israel DNA database has recently started to conduct familial searches (FS). We adopted the CODIS pedigree strategy for FS, which is used in the Unidentified Human Remains (UHR) database and implemented it into the criminal forensic database. This strategy is based on Kinship analysis performed in pedigrees containing DNA profiles from the crime scene designated "unknown," that are then searched against the entire suspects database. A list of candidates is produced and ranked by Joint Pedigree Likelihood Ratio (JPLR). Traditional Y-STR characterizing and mitochondrial sequencing can be performed in order to further minimize the list. Our novel strategy consists of an additional pedigree analysis aimed at prioritizing potential candidates from the candidate list: a Test Pedigree Tree (TPT). Candidates ranked high on the JPLR list can be verified or eliminated from the list by using other close family members included in the database. To further validate this novel strategy, we describe two cases where implementation of this strategy led to a successful match and solved the crime.

Improved amplification results following episodes of failure to amplify at the Amelogenin Locus using PowerPlex® ESI 16 Fast System.

In 2012 the Israel Police DNA Casework laboratory adopted the 16 STR PowerPlex® ESI kit for routine use. The Promega Company updated this kit and developed the PowerPlex® ESI 16 Fast System in which all autosomal primer pairs remained identical to the original set, except at the amelogenin site. The master mix was improved and optimized which allowed for direct, faster and more robust amplification. Prior to implementing the PowerPlex® ESI 16 Fast System in our lab, we conducted a preliminary assay where 213 casework samples were amplified using the new kit. These samples had previously been extracted by one of two extraction kits employed by our lab. (the PrepFiler ExpressTM and PrepFiler BTATM Forensic DNA Extraction Kits). The amplification results from these samples were compared to samples amplified using the original PowerPlex® ESI 16 kit. Multiple incidents of failure to amplify at the amelogenin locus were noted using the new system with the recommended protocol at a rate of 13% (28 of 213 samples). Experiments were performed to understand whether these amplification failures could be a result of primer binding site mutations, extraction method reagents and/or inhibitors. The conclusions reached following these experiments, in conjunction with consultation with the manufacturer, led to the trial of a modified amplification protocol where the suggested annealing temperature was reduced by 2 degrees. To evaluate the efficiency of this altered protocol, a comparison study was undertaken where 88 additional casework samples were chosen and amplified using both the modified 58°C and the recommended 60°C annealing temperatures. We concluded that the most effective method in our laboratory for achieving a consistent and balanced amplification at the amelogenin locus was to reduce the annealing temperature from the manufacturer's recommended 60°C to 58°C. This modification resulted in a reduction of the failure to amplify at the amelogenin locus from 13% (28/213) to 1.1% (1/88) without any observed changes to the autosomal STR amplification results.