TrueAllele solves uninterpretable DNA in mother and daughter double homicide

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TrueAllele validation paper chosen as a 2020 Noteworthy Article by the Journal of Forensic Sciences

Cybergenetics peer-reviewed Journal of Forensic Sciences (JFS) article, "Validating TrueAllele® Interpretation of DNA Mixtures Containing up to Ten Unknown Contributors," has been chosen by the JFS Associate Editors and Editor-in-Chief as a 2020 Noteworthy Article.

A link to the article is featured in a special 2020 JFS Noteworthy Articles collection on the JFS homepage. The article is also among those promoted at the 2021 American Academy of Forensic Sciences (AAFS) Virtual Exhibit, with free access for attendees throughout February and March of 2021.

The authors of the noteworthy article are Dr. David Bauer, Dr. Nasir Butt, Jennifer Bracamontes, and Dr. Mark Perlin.

"Most DNA evidence is a mixture of two or more people," they wrote. "Cybergenetics TrueAllele system uses Bayesian computing to separate genotypes from mixture data, and compare genotypes to calculate likelihood ratio (LR) match statistics.

"This validation study examined the reliability of TrueAllele computing on laboratory-generated DNA mixtures containing up to ten unknown contributors. Using log(LR) match information, the study measured sensitivity, specificity, and reproducibility. These reliability metrics were assessed under different conditions, including varying the number of assumed contributors, statistical sampling duration, and setting known genotypes.

"The main determiner of match information and variability was how much DNA a person contributed to a mixture. Observed contributor number based on data peaks gave better results than the number known from experimental design. The study found that TrueAllele is a reliable method for analyzing DNA mixtures containing up to ten unknown contributors."

Other results include the impact of "peeling" away multiple layers of genotype contributors, and how the number of input data peaks affects the LR. Mixture composition followed a randomized design, with two TrueAllele interpretation groups independently analyzing the same STR data using their own in-house computer systems.

Co-author Dr. Nasir Butt, DNA Technical Manager and Supervisor of the Cuyahoga County Regional Forensic Science Laboratory, conducted the independent TrueAllele testing in his Cleveland, Ohio facility.

Testing the TrueAllele computer system on DNA mixture data prepared by Dr. Butt, the study reached some notable conclusions.

"Separated genotypes follow a predictive empirical law. When compared with a person's genotype, their log(LR) match information is proportional to the logarithmic amount of DNA contributed by the person until a maximum LR is reached. The results were consistent with a linear relationship between DNA amount and identification information.

"The data showed that contributor DNA quantity determines mixture information and its variability. The 2016 President's Council of Advisors on Science and Technology (PCAST) policy report suggested limiting DNA mixture usage based on contributor number and mixture weight. The empirical validation study underscores why this forensic policy proposal is scientifically unfounded."

Some forensic workers introduce "ground truth" into their testing. "However," wrote the authors, "the study supports interpreting evidence based on data observation, not unknowable facts. A small amount of contributor DNA may suffer allele dropout or imbalance, and so express its genotype unfaithfully – or not at all – in the STR data. The correct inference is a probability distribution that quantifies this genotype uncertainty, independently of what we believe we 'know' should be there. Contextual bias can only diminish forensic objectivity."

The authors note, "Empirical testing is the basis of scientific and legal reliability. Validation studies can test laboratory generated data, or casework field data. Both are needed, since methods that excel in the lab may fail in the field. For transparency and respect for Sixth Amendment rights, defendants should have an opportunity to test the forensic casework methods and data used against them."

Cybergenetics makes its TrueAllele software available to defendants at no charge, so that they can conduct their own testing.

Forty validation studies have empirically tested the TrueAllele forensic genotyping system. Seven were published in peer-reviewed journals. "This study extends that testing," conclude the authors, "establishing TrueAllele reliability on mixtures containing up to ten unknown contributors."

Cybergenetics has made this JFS 2020 Noteworthy Article open access, available to the forensic science community and the general public. The TrueAllele validation study can be freely read or downloaded without charge.


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