Trace DNA Transfer in Co-Working Spaces: The Importance of Background DNA Analysis.

The presence of background DNA (bgDNA) can hinder the evaluation of DNA evidence at the activity level, especially when the suspect is expected to be retrieved due to their habitual occupation of the investigated environment. Based on real-life casework circumstances, this study investigates the prevalence, composition, origin, and probable transfer routes of bgDNA found on personal items in situations where their owner and person of interest (POI) share the same workspace. Baseline values of bgDNA were evaluated on the participants' personal items. Secondary and higher degree transfer scenarios of non-self DNA deposition were also investigated. The DNA from co-workers and co-inhabiting partners can be recovered from an individual's personal belongings. Non-self DNA present on the hands and deposited on a sterile surface can generate uninformative profiles. The accumulation of foreign DNA on surfaces over time appears to be crucial for the recovery of comparable profiles, resulting in detectable further transfer onto other surfaces. For a thorough evaluation of touch DNA traces at the activity level, it is necessary to collect information not only about DNA transfer probabilities but also about the presence of the POI as part of the 'baseline' bgDNA of the substrates involved.

Estimation of Human Chronological Age from Buccal Swab Samples through a DNA Methylation Analysis Approach of a Five-Locus Multiple Regression Model.

Recent advancements in forensic genetics have facilitated the extraction of additional characteristics from unidentified samples. This study delves into the predictive potential of a five-gene (ELOVL2, FHL2, KLF14, C1orf132, and TRIM59) methylation rate analysis for human age estimation using buccal swabs collected from 60 Italian volunteers. The methylation levels of specific CpG sites in the five genes were analyzed through bisulfite conversion, single-base extension, and capillary electrophoresis. A multivariate linear regression model was crafted on the training set, then the test set was employed to validate the predictive model. The multivariate predictive model revealed a mean absolute deviation of 3.49 years in the test set of our sample. While limitations include a modest sample size, the study provides valuable insights into the potential of buccal swab-based age prediction, aiding in criminal investigations where accurate age determination is crucial. Our results also highlight that it is necessary to investigate the effectiveness of predictive models specific to biological tissues and individual populations, since models already proven effective for other populations or different tissues did not show the same effectiveness in our study.

Forensic Age Estimation through a DNA Methylation-Based Age Prediction Model in the Italian Population: A Pilot Study.

DNA methylation is one of the epigenetic marks which has been studied intensively in recent years for age predicting purposes in the forensic area. In order to integrate age prediction into routine forensic workflow, the purpose of this study was to standardize and optimize a DNA methylation-based protocol tailored to the Italian context. A previously published protocol and age-predictive method was implemented for the analysis of 84 blood samples originating from Central Italy. The study here presented is based on the Single Base Extension method, considering five genes: ELOVL2, FHL2, KLF14, C1orf132, now identified as MIR29B2C, and TRIM59. The precise and specific steps consist of DNA extraction and quantification, bisulfite conversion, amplification of converted DNA, first purification, single base extension, second purification, capillary electrophoresis, and analysis of the results to train and test the tool. The prediction error obtained, expressed as mean absolute deviation, showed a value of 3.12 years in the training set and 3.01 years in the test set. Given that population-based differences in DNA methylation patterns have been previously reported in the literature, it would be useful to further improve the study implementing additional samples representative of the entire Italian population.

Assessing DNA Degradation through Differential Amplification Efficiency of Total Human and Human Male DNA in a Forensic qPCR Assay.

The assessment of degradation is crucial for the analysis of human DNA samples isolated from forensic specimens. Forensic quantitative PCR (qPCR) assays can include multiple targets of varying amplicon size that display differential amplification efficiency, and thus different concentrations, in the presence of degradation. The possibility of deriving information on DNA degradation was evaluated in a forensic qPCR assay not specifically designed to detect DNA fragmentation, the Plexor HY (Promega), by calculating the ratio between the estimated concentrations of autosomal (99 bp) and Y-chromosomal (133 bp) targets ("[Auto]/[Y]"). The [Auto]/[Y] ratio measured in 57 formalin-fixed, paraffin-embedded samples was compared to a quality score (QS) calculated for corresponding STR profiles using quantitative data (allele peak height). A statistically significant inverse correlation was observed between [Auto]/[Y] and QS (R = -0.65, p < 0.001). The [Auto]/[Y] values were highly correlated (R = 0.75, p < 0.001) with the "[Auto]/[D]" values obtained using the PowerQuant (Promega) assay, expressly designed to detect DNA degradation through simultaneous quantification of a short (Auto) and a long (D) autosomal target. These results indicate that it is possible to estimate DNA degradation in male samples through Plexor HY data and suggest an alternative strategy for laboratories lacking the equipment required for the assessment of DNA integrity through dedicated qPCR assays.

The Usefulness of qPCR Data for Sample Pre-Assessment and Interpretation of Genetic Typing Results.

DNA quantification is a crucial step in the STR typing workflow for human identification purposes. Given the reaction's nature, qPCR assays may be subjected to the same stochastic effects of traditional PCR for low-input concentrations. The study aims to evaluate the precision of the PowerQuant® (Promega) kit assay measurements and the degree of variability for DNA templates falling below the optimal threshold of the PowerPlex® ESX-17 Fast STR typing kit (Promega). Five three-fold dilutions of the 2800 M control DNA (Promega) were set up. Each dilution (concentrations: 0.05, 0.0167, 0.0055, 0.00185, and 0.000617 ng/µL) was quantified and amplified in four replicates. Variability for qPCR results, STR profile completeness, and EPGs' peak height were evaluated. The qPCR-estimated concentration of casework samples was correlated with profile completeness and peak intensity, to assess the predictive value of qPCR results for the successful STR typing of scarce samples. qPCR was subjected to stochastic effects, of which the degree was inversely proportional to the initial input template. Quantitation results and the STR profile's characteristics were strongly correlated. Due to the intrinsic nature of real casework samples, a qPCR-derived DNA concentration threshold for correctly identifying probative STR profiles may be difficult to establish. Quantitation data may be useful in interpreting and corroborating STR typing results and for clearly illustrating them to the stakeholders.

Direct and Secondary Transfer of Touch DNA on a Credit Card: Evidence Evaluation Given Activity Level Propositions and Application of Bayesian Networks.

In a judiciary setting, questions regarding the mechanisms of transfer, persistence, and recovery of DNA are increasingly more common. The forensic expert is now asked to evaluate the strength of DNA trace evidence at activity level, thus assessing if a trace, given its qualitative and quantitative features, could be the result of an alleged activity. The present study is the reproduction of a real-life casework scenario of illicit credit card use by a co-worker (POI) of its owner (O). After assessing the shedding propensity of the participants, differences in DNA traces' qualitative and quantitative characteristics, given scenarios of primary and secondary transfer of touch DNA on a credit card, a non-porous plastic support, were investigated. A case-specific Bayesian Network to aid statistical evaluation was created and discrete observations, meaning the presence/absence of POI as a major contributor in both traces from direct and secondary transfer, were used to inform the probabilities of disputed activity events. Likelihood Ratios at activity level (LRα) were calculated for each possible outcome resulting from the DNA analysis. In instances where only POI and POI plus an unknown individual are retrieved, the values obtained show moderate to low support in favour of the prosecution proposition.

Establishing a missing person DNA Biobank as a form of human rights protection.

Nowadays, organ transplantation is considered an established medical practice that, every year, improves the quality of life of thousands of patients. However, the increasing demands for kidney transplantation are in contrast with the global lack of organs. The imbalance between supply and demand for organs has created the basis for a highly profitable black market, placing illicit organ trafficking in the broader context of human trafficking. Currently, thanks to the advancements of the analytical techniques used in laboratories, forensic genetics is able to discriminate the geographical origin of genetically distinct populations. The recent availability of genetic data regarding many populations of the world and the concomitant development of technologies and methodologies that are appropriate for the study of panels of STRs and SNPs are fundamental resources in this direction. This type of analyses, together with the creation of missing person DNA databases, may be used in cases of dubious origin of organs or in transplantation cases in which clear and comprehensive medical records of patients and donors are not available. It can also establish a scientific tool useful to contrast the illegal traffic of human kidneys. In this article, we will discuss biological and ethical aspects of this interesting perspective.