RESUMEN
The ability to associate a contributor with a specific body fluid in a crime stain can aid casework investigation. The detection of body fluids combined with DNA analyses may supply essential information, but as the two tests are independent, they may not be associated. Recently, the analysis of coding region SNPs (cSNPs) within the RNA transcript has been proven to be a promising method to face this challenge. In this study, we performed targeted RNA sequencing of 158 samples (boxershorts, fingernail swabs and penile swabs) collected from 12 couples at different time points post-intimate contact and after non-intimate contact, using the Ion S5™ System and BFID-cSNP-6F assay. The aim of the study was to compare the performance of the MPS and CE methods in the detection of mRNA markers, and to associate body fluids with contributors by their cSNP genotypes. The results of the study show a lower success rate in the detection of vaginal mucosa by the MPS compared to the CE method. However, the additional information obtained with the cSNP genotypes could successfully associate body fluids with contributors in most cases.
Asunto(s)
Líquidos Corporales , Femenino , Humanos , ARN Mensajero/genética , Genotipo , Secuencia de BasesRESUMEN
In sexual assault cases, it can be challenging to identify the type of body fluids/ cell types present in a crime scene sample, especially the origin of epithelial cells. Therefore, more labs are applying mRNA body fluid analysis for saliva, skin and vaginal mucosa markers. To address activity level propositions, it is necessary to assign probabilities of transfer, persistence, prevalence and recovery of DNA and mRNA markers. In this study we analysed 158 samples (fingernail swabs, penile swabs and boxershorts) from 12 couples collected at different time points post intimate contact and after non-intimate contact in order to detect DNA from the person of interest (POI) and mRNA vaginal mucosa markers. Samples were DNA and RNA co-extracted and analysed with PowerPlex®Fusion 6C System and 19-plex mRNA primer mix respectively, using Endpoint PCR and the CE platform. Vaginal mucosa was detected up to 36 h post intimate contact, but also detected in one non-intimate contact sample. In 94% of intimate contact and 50 % of non-intimate contact samples the DNA results support the proposition that POI is the donor (LR ≥ 10,000). There was a strong association between the detection of vaginal mucosa and the average RFU value of the POI. The data were used to instantiate a comprehensive Bayesian network to evaluate the evidence at activity level, given alternate propositions conditioned upon indirect or direct transfer events. It is shown that the value of the evidence is mainly affected by the high DNA quantity (measured as mean RFU) that is recovered from the POI. The detection of vaginal mucosa had low impact upon the resultant likelihood ratio.
Asunto(s)
Dermatoglifia del ADN , ADN , Teorema de Bayes , ADN/genética , Dermatoglifia del ADN/métodos , Femenino , Humanos , Membrana Mucosa/química , ARN Mensajero/genéticaRESUMEN
The shedder status of an individual may be important to consider in the context of DNA transfer, persistence and recovery and in Bayesian networks where a person's shedder status may have an impact on the outcome. In this study we compared two methods to determine shedder status: the handheld tube (HH) method and a fluorescent cell count (CC) method. A poor association was observed between the numbers of detected cells in a fingerprint using the CC method and the strength of the DNA result with the HH method. The 20 participants were classified into low (25%), medium (50%) and high (25%) shedders based on the HH method. While the low and high shedders showed a good consistency between the replicates, the medium shedders varied more and have to be considered more carefully as they may act as either a high or a low shedder in an event of DNA transfer.
Asunto(s)
Recuento de Células/métodos , Dermatoglifia del ADN , Dermatoglifia , Manejo de Especímenes/instrumentación , Femenino , Colorantes Fluorescentes , Genética Forense/métodos , Humanos , Masculino , Microscopía Fluorescente , Reacción en Cadena de la PolimerasaRESUMEN
Data from all sexual assault cases analysed at the Section of Forensic Biology at Oslo University Hospital in the period 2013-2015 were reviewed to study transfer and persistence of cells deposited on the body. Data were recorded on detection of both sperm and epithelial cells. The final dataset consist of 2141 samples from 765 cases. In this study "positive findings" refer to evidence to support the proposition that the DNA profile was contributed by the POI and do not only correspond to detection of cell type, e.g. sperm cells. Positive findings from analysis of sperm cells could be detected in samples collected up to 72â¯h after deposition, and was less frequently detected in oral swabs were the longest observed persistence time was 12â¯h. Positive findings from analysis of epithelial cells were observed up to 43â¯h after deposition. A high success rate was observed from penile swabs collected within 24â¯h of the incidence demonstrating the importance of collecting and analysing such samples in cases where no semen is detected.
Asunto(s)
Dermatoglifia del ADN , ADN/aislamiento & purificación , Células Epiteliales/citología , Delitos Sexuales , Espermatozoides/citología , Células Epiteliales/química , Femenino , Genética Forense/métodos , Humanos , Masculino , Boca/citología , Reacción en Cadena de la Polimerasa , Recto/citología , Estudios Retrospectivos , Piel/citología , Manejo de Especímenes , Espermatozoides/química , Factores de Tiempo , Vagina/citología , Vulva/citologíaRESUMEN
As the profiling systems used in forensic analyses have become more sensitive in recent years, the risk of detecting a contamination in a DNA sample has increased proportionally. This requires more stringent work protocols and awareness to minimize the chance of contamination. Although there is high consciousness on contamination and best practice procedures in forensic labs, the same requirements are not always applied by the police. In this study we have investigated the risk of contamination from police staff. Environmental DNA was monitored by performing wipe tests (sampling of hot spots) at two large police units (scenes of crime departments). Additionally, the DNA profiles of the scenes of crime officers were compared to casework samples that their own unit had investigated in the period of 2009-2015. Furthermore, a pilot study to assess whether DNA from the outside package of an exhibit could be transferred to a DNA sample was carried out. Environmental DNA was detected in various samples from hot spots. Furthermore, 16 incidences of previously undetected police-staff contamination were found in casework that had been submitted between 2009 and 2015. In 6 cases the police officers with a matching DNA profile reported that they had not been involved with the case. We have demonstrated that DNA from the outside package can be transferred to an exhibit during examination. This experience demonstrates that when implementing the new multiplex systems, it is important to ensure that 'best practice' procedures are upgraded, and appropriate training is provided in order to ensure that police are aware of the increased contamination risks.