The problem of DNA contamination in forensic case work—How to get rid of unwanted DNA?

The PCR technique has become a powerful and very sensitive tool in a broad field of research, that is, molecular biology, medical diagnostics, population genetics, ancient DNA analysis and forensic casework.However, the high sensitivity down to single molecules can easily cause false-positive PCR results due to different types of contamination. In this study, artificial DNA contaminations (saliva and pure DNA) were treated with UV irradiation and other decontamination procedures. A satisfactory DNA removal could not be achieved, emphasizing the necessity of contamination avoidance.     

The effect of NucleoSpin® Forensic Filters on DNA recovery from trace DNA swabs

Forensic DNA profiling is a globally accepted method for human identification, however, obtaining full DNA profiles from trace DNA can be challenging. The optimal recovery of DNA from trace DNA swabs is therefore crucial. Methods for extracting DNA from swabs often make use of a spin basket combined with a centrifugation step, to enhance the release of cells from the swab prior to DNA extraction. The NucleoSpin® Forensic Filter (Macherey-Nagel, Düren) is a type of spin basket, but it has not been thoroughly assessed on trace DNA samples. This study aimed to assess if the inclusion of the NucleoSpin® Forensic Filter significantly improved DNA recovery and DNA profiling success from cotton and flocked swabs used to collect trace DNA and buccal cells (control). Buccal cells and trace DNA samples were collected from 25 volunteers using each swab type (cotton and flocked) in duplicate. DNA was extracted from the samples using the NucleoSpin® DNA Forensic kit, one set with, and the other set without, NucleoSpin® Forensic Filters. DNA concentration was assessed using real time PCR, and DNA profiling was done using the PowerPlex® ESX 16 system. The inclusion of the NucleoSpin® Forensic Filters significantly improved DNA concentration for buccal cells that were collected using flocked swabs (p = 0.035). However, no significant differences were noted for trace DNA samples for either swab type. There was also no significant difference in DNA profiling success when NucleoSpin® Forensic Filters were used, regardless of swab and sample type. These results may be helpful for laboratories that are considering the NucleoSpin® Forensic Filters in the DNA extraction workflow, particularly for trace DNA samples.     

AutoMate Express™ forensic DNA extraction system for the extraction of genomic DNA from biological samples

Abstract: The AutoMate Express? Forensic DNA Extraction System was developed for automatic isolation of DNA from a variety of forensic biological samples. The performance of the system was investigated using a wide range of biological samples. Depending on the sample type, either PrepFiler? lysis buffer or PrepFiler BTA? lysis buffer was used to lyse the samples. After lysis and removal of the substrate using LySep? column, the lysate in the sample tubes were loaded onto AutoMate Express? instrument and DNA was extracted using one of the two instrument extraction protocols. Our study showed that DNA was recovered from as little as 0.025 μL of blood. DNA extracted from casework‐type samples was free of detectable PCR inhibitors and the short tandem repeat profiles were complete, conclusive, and devoid of any PCR artifacts. The system also showed consistent performance from day‐to‐day operation.     

DNA identification of skeletal remains by investigator’s intuition

In June 2006 a decapitated woman was found in a parking area of the motorway in the area of Prato (Florence). Since the body was beheaded and no victim’s documents or objects were present at the crime scene, identification at that time was impossible. However, DNA profile from woman’s bones were collected. In the same year (2003), a mother had reported her daughter's disappearance but the two events were not related at that time. About ten years later the mother’s DNA profile was finally acquired for a genetic identification of another girl’s body found in the Ferrara area. These genetic profiles were completely discordant. All these genetic comparisons were carried out on behalf of the prosecutors of the cities involved in the findings of the bodies and in the disappearance complaints, but due to the lack of a database the events remained disconnected. In January 2017, the head of the scientific police of Prato who had followed the investigation and questioned the mother of the missing girl found about ten years later, suggested to the magistrate to order the comparison of the mother's DNA with the genetic profile of the bones found in 2006. This comparison finally allowed the identification of the missing daughter.This story highlights the importance of having forensic DNA database to search for missing persons and how the investigator's intuition can play a key role in resolving criminal cases. In fact, databases of unknown bodies and relatives of missing persons were created in Italy as a part of national DNA database just at the beginning of 2018.     

Contamination of forensic DNA evidence in the light of Hungarian court decisions – A review of 25 years

The evaluation of forensic DNA expert opinions (in some countries expert witness testimonies) and the way it affects criminal judgement is of paramount importance. We have selected one of the largest challenges when it comes to the evaluation of forensic DNA evidence, contamination of DNA samples, and examined how it influences the decisions judges make about the credibility of DNA evidence in Hungary.     

Detection and analysis of DNA mixtures with the MiSeq FGx®

Recognizing and interpreting mixtures are challenges that occur frequently in forensic casework. Therefore, any new analysis methods that are implemented must handle the challenges of mixed forensic samples. Next generation sequencing offers advantages over capillary electrophoresis in amplicon multiplexing and degraded sample analysis; however, advantages with mixed samples rely heavily on the advancement of user-friendly analysis software. This research analyzed samples with the ForenSeq™ DNA Signature Prep Kit on the MiSeq FGx® and compared them with the GlobalFiler™ STR Kit for capillary electrophoresis. Metrics tested for both chemistries included concordance, limits of detection, and mixture analysis. Data analysis for mixture samples was completed with the MixtureAce™ plug-in and ArmedXpert™ software. Next generation sequencing offered distinct advantages in limits of detection and isoallele heterozygosity but suffered from increased variability in stutter and allele count ratios compared to capillary electrophoresis.     

Implementation of Prep-n-Go™ Buffer for DNA extraction from buccal swabs

The efficacy of two extraction methods; room temperature and heat protocols was assessed for buccal swabs using the Prep-n-Go™ Buffer. DNA was extracted from buccal swabs using both extraction methods and their effectiveness to produce good quality DNA profiles was evaluated. Heat protocol was found to yield more DNA, however room temperature protocol produced better quality DNA profiles with fewer artefacts when the samples from both extraction methods were amplified directly without any normalisation with the VeriFiler™ Express PCR Amplification Kit.     

Two or three contributors of DNA mixtures? – Some practical considerations

The number of contributors is hard to determine in DNA mixture profiles. Here, we deal with the special but frequent case that either two or three contributors are possible. In fact, it might happen that two contributors can explain the number of alleles seen but that three contributors are necessary if a specific person of interest is to be included in the mixture. Then the likelihood ratio assuming two contributors will be zero while the likelihood ratio for three contributors may be large. We evaluate this situation and offer suggestions on how to arrive at an overall likelihood ratio. To exemplify our line of reasoning we use an example proposed by Biedermann, Taroni and Thompson.     

Individual identification of cats and dogs using mitochondrial DNA tandem repeats?

Cats and dogs are very common animals in the human environment. In Switzerland, one in five households owns a cat or a dog. Their hairs are very easily transferred and could be used as a frequent trace evidence. Using DNA analysis, identification of these animals should be possible as it is in human identification. However, most of the time, no nuclear DNA can be recovered from the hair. It is therefore necessary to rely on mtDNA. Cats and dogs have tandemly repeated sequences in their mtDNA control region. In this study, the authors show that these tandem repeats are very polymorphic but are also the source of a very high level of heteroplasmy. The authors, therefore, examined if this might prevent their use in forensic identification.     

DNA作证

基因时代到来以后,令各国政府头疼的犯罪问题可能会销声匿迹。为什么呢?因为那时的警察应用基因侦破技术,只要在现场发现很微小的罪犯遗留下的“基因线索”,就能得到罪犯完整的DNA序列,然后在人类基因资料库中轻而易举地查出罪犯……     

DNA画像

2010年1月27日夜里11点15分,美国旧金山警方接获报案电话。待警察赶到旧金山唐人街奠拉加街的—户两层别墅内时,发现华裔屋主李文贵在一楼已经中枪死亡,两名劫犯也已经逃逸。李文贵死时也手持一把手枪,屋内有枪战的痕迹,除了李文贵身旁有大摊血迹外,     

Background Levels of Salivary-α-amylase Plus Foreign DNA in Cases of Oral Intercourse: a Female Perspective

Saliva plus DNA from a suspect is commonly encountered in sexual assault cases on bodily swabs. However, without background knowledge, the weight of this evidence is unknown. It may indicate the presence of saliva resulting from cunnilingus, or it may represent indirect transfer. In this study, females who refrained from cunnilingus donated 43 items of underwear and 19 vaginal swabs. The samples were subjected to Phadebas^®, RSID^™-Saliva and mRNA profiling and were subsequently DNA-profiled to determine the prevalence of background saliva in the female population. The results report that 15.8% of females who refrained from cunnilingus were positive for saliva and a further 10.5% also had DNA from unknown source(s). These findings of the rate of indirect transfer were evaluated with the Bayesian approach, and it was found that the evidence of saliva plus a high foreign DNA source adds moderately strong support to the allegation of cunnilingus.     

Science in the Jury Box: Jurors’ Comprehension of Mitochondrial DNA Evidence

Questions about how jurors understand and apply scientific evidence were addressed in a mock jury study in which 480 jury pool members watched a videotaped mock trial that included expert testimony about mitochondrial DNA (mtDNA) evidence purportedly linking a defendant to a crime. Collectively, jurors showed moderately good comprehension of the mtDNA evidence, although some made definitional and inferential errors. Comprehension was better among jurors with higher educational attainment and more mathematics and science courses. Lower comprehension was associated with jurors’ reservations about science and concerns about the contamination of mtDNA evidence. The results suggest that most jurors are capable of comprehending and employing scientific evidence presented during trial, although errors and doubts about the evidence should be anticipated.     

Was elusive carnivore a panther? DNA typing of faeces reveals the mystery

In this study, we report the findings of a recent case in which the officials of an Indian zoo claimed that an animal, possibly a carnivore, is periodically visiting the zoo from a nearby vast forest area and causing panic in zoo and nearby villages. They collected some elusive faecal material from the vicinity of an herbivore enclosure. Looking to the pugmarks found in that area and faecal matter ceased, the officials could not decide whether it was a lioness, a tiger or a panther. We resolved this mystery by DNA-based analysis of the faecal material, using our recently developed novel universal primers to amplify and sequence a specific fragment of mitochondrial cytochrome b gene. The findings of the DNA-based analyses were confirmed after few days when the zoo officials trapped the animal of same species as suggested in our report. The potential of our procedure to investigate the cases related to wildlife offence is discussed.     

DNA甲基化在法医DNA分析中的应用

表观遗传学在生命的发生、发展过程中起着十分重要的作用。DNA甲基化作为表观遗传的一个重要方面,不仅参与多种基因的表达调控,与机体的发育、肿瘤发生等密切相关,而且具有可遗传性、相对稳定性、亲缘特异性、基因组中含量丰富等特点,已证实适用于法医DNA分析。本文对近年来DNA甲基化在印迹基因、同卵双生子鉴定、年龄、性别推断方面的研究与应用进行回顾与综述,以期为在法医学及相关领域中应用提供参考。     

法医DNA分型 第一讲 DNA多态性基本原理

DNA (脱氧核糖核酸 )是生物遗传物质。DNA分型技术在法医物证鉴定中应用日益广泛 ,在各类重大刑事案件的侦破中发挥了越来越重要的作用。近 10多年 ,是法医学发展最快的时期 ,DNA分型技术跨了两大步 :1985年建立的第一代分型技术———DNA指纹 ,实现了物证鉴定从否定到认定的历史性转变 ;进入 90年代 ,PCR (聚合酶链反应 )技术问世 ,可以在体外完成扩增复制靶DNA片段的全过程 ,是生命科学一项划世纪的进展。以PCR为基础的第二代DNA分型技术在检测灵敏度上有重大突破 ,解决了半个多世纪以来困扰法医的微量、陈旧、腐败检材鉴定的难题。DNA分型的高科技 ,以其无可争议的认定或否定的鉴定结论 ,为法庭提供确凿的证据 ,成为打击犯罪的有力武器。从本期起 ,对《法医DNA分型》进行专题讲座 ,将分期介绍DNA多态性基本原理 ,DNA分型结论的评估 ,法医DNA分型技术与方法 ,以及DNA分析技术展望等四个部分 ,以飨读者     

DNA analysis and the Freedom of Information Act: information or invasion?

This note explores the possibility of release of an individual's DNA analysis to any person who requests it through the Freedom of Information Act (FOIA), after an individual's post-aircraft accident DNA profile has been developed by the Federal Aviation Administration's (FAA) Civil Aerospace Medical Institute (CAMI). It analyzes whether the request would fall under the FOIA's 552(b)(6) exemption, which weighs a person's privacy interest against any public interest in such information, or if the release would constitute a "clearly unwarranted invasion of personal privacy."     

法医DNA实验室的DNA污染和防范

DNA污染是产生DNA鉴定结论错误的重要因素,法医DNA实验室要努力去解决这一问题。DNA污染有自身污染、交叉污染、PCR污染3种。法医DNA实验室要采取实验室分区、严格检验操作步骤、对试剂及消耗材料进行质量控制等方法防止发生DNA污染,采取设置对照样本、核查DNA结果、建立DNA排查数据库等方法监测和发现DNA污染。     

A preliminary assessment of the effect of PreCR™ DNA repair treatment on mixture ratios in two person mixtures

In this study, DNA extracted from known buccal samples was combined into two component mixture samples. These were subjected to UV exposure prior to their amplification with the Promega PowerPlex® 16HS amplification kit, and subsequent capillary electrophoresis on the ABI 3130xl instrument. Damaged samples were subjected to enzymatic repair treatment and retested to assess the amount of repair. Data showed that there is fidelity associated with the application with profile concordance after its use, and a corresponding increase in the amount of recovered alleles post damage. Results also showed changes in the stochastic relationship between mixture components that appear to be induced by the repair process itself. The mixture ratios of DNA samples were altered from an approximate original 1:3 ratio, to a ratio of 1:2 or greater. This variation can have a significant effect regarding the ability to reliably de-convolute DNA mixtures that have been subjected to the repair process.