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Kim BM, Park SU, Lee HY. Comparative analysis of SNaPshot and massively parallel sequencing for body fluid-specific DNA methylation markers. Electrophoresis 2024. [PMID: 39119735 DOI: 10.1002/elps.202400037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2024] [Revised: 07/05/2024] [Accepted: 07/27/2024] [Indexed: 08/10/2024]
Abstract
The identification of tissue-specific differentially methylated regions has significantly contributed to the field of forensic genetics, particularly in body fluid identification crucial for linking evidence to crimes. Among the various approaches to analyzing DNA methylation, the SNaPshot assay has been popularly studied in numerous researches. However, there is a growing interest in exploring alternative methods such as the use of massively parallel sequencing (MPS), which can process a large number of samples simultaneously. This study compares SNaPshot and MPS multiplex assays using nine cytosine-phosphate-guanine markers for body fluid identification. As a result of analyzing 112 samples, including blood, saliva, vaginal fluid, menstrual blood, and semen, both methods demonstrated high sensitivity and specificity, indicating their reliability in forensic investigations. A total of 92.0% samples were correctly identified by both methods. Although both methods accurately identified all blood, saliva, and semen samples, some vaginal fluid samples showed unexpected methylation signals at nontarget loci in addition to the target loci. In the case of menstrual blood samples, due to their complexity, independent typing criteria were applied, and successful menstrual blood typing was possible, whereas a few samples showed profiles similar to vaginal fluid. The MPS method worked better in vaginal fluid samples, and the SNaPshot method performed better in menstrual blood samples. This study offers valuable insights into body fluid identification based on the characteristics of the SNaPshot and MPS methods, which may help in more efficient forensic applications.
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Affiliation(s)
- Bo Min Kim
- Department of Forensic Medicine, Seoul National University College of Medicine, Seoul, South Korea
| | - Sang Un Park
- Department of Forensic Medicine, Seoul National University College of Medicine, Seoul, South Korea
| | - Hwan Young Lee
- Department of Forensic Medicine, Seoul National University College of Medicine, Seoul, South Korea
- Institute of Forensic and Anthropological Science, Seoul National University College of Medicine, Seoul, South Korea
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2
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So MH, Lee JE, Lee HY. Strategies to deal with genetic analyzer-specific DNA methylation measurements. Electrophoresis 2024; 45:906-915. [PMID: 38488745 DOI: 10.1002/elps.202300185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 02/25/2024] [Accepted: 03/02/2024] [Indexed: 05/23/2024]
Abstract
Targeted bisulfite sequencing using single-base extension (SBE) can be used to measure DNA methylation via capillary electrophoresis on genetic analyzers in forensic labs. Several accurate age prediction models have been reported using this method. However, using different genetic analyzers with different software settings can generate different methylation values, leading to significant errors in age prediction. To address this issue, the study proposes and compares four methods as follows: (1) adjusting methylation values using numerous actual body fluid DNA samples, (2) adjusting methylation values using control DNAs with varying methylation ratios, (3) constructing new age prediction models for each genetic analyzer type, and (4) constructing new age prediction models that could be applied to all types of genetic analyzers. To test the methods for adjusting values using actual body fluid DNA samples, previously reported adjusting equations were used for blood/saliva DNA age prediction markers (ELOVL2, FHL2, KLF14, MIR29B2CHG/C1orf132, and TRIM59). New equations were generated for semen DNA age prediction markers (TTC7B, LOC401324/cg12837463, and LOC729960/NOX4) by drawing polynomial regression lines between the results of the three types of genetic analyzers (3130, 3500, and SeqStudio). The same method was applied to obtain adjustment equations using 11 control DNA samples. To develop new age prediction models for each genetic analyzer type, linear regression analysis was conducted using DNA methylation data from 150 blood, 150 saliva, and 62 semen samples. For the genetic analyzer-independent models, control DNAs were used to formulate equations for calibrating the bias of the data from each genetic analyzer, and linear regression analysis was performed using calibrated body fluid DNA data. In the comparison results, the genetic analyzer-specific models showed the highest accuracy. However, genetic analyzer-independent models through bias adjustment also provided accurate age prediction results, suggesting its use as an alternative in situations with multiple constraints.
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Affiliation(s)
- Moon Hyun So
- Department of Forensic Medicine, Seoul National University College of Medicine, Seoul, South Korea
| | - Ji Eun Lee
- Department of Forensic Medicine, Seoul National University College of Medicine, Seoul, South Korea
| | - Hwan Young Lee
- Department of Forensic Medicine, Seoul National University College of Medicine, Seoul, South Korea
- Institute of Forensic and Anthropological Science, Seoul National University College of Medicine, Seoul, South Korea
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3
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Castagnola MJ, Medina-Paz F, Zapico SC. Uncovering Forensic Evidence: A Path to Age Estimation through DNA Methylation. Int J Mol Sci 2024; 25:4917. [PMID: 38732129 PMCID: PMC11084977 DOI: 10.3390/ijms25094917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2024] [Revised: 04/27/2024] [Accepted: 04/28/2024] [Indexed: 05/13/2024] Open
Abstract
Age estimation is a critical aspect of reconstructing a biological profile in forensic sciences. Diverse biochemical processes have been studied in their correlation with age, and the results have driven DNA methylation to the forefront as a promising biomarker. DNA methylation, an epigenetic modification, has been extensively studied in recent years for developing age estimation models in criminalistics and forensic anthropology. Epigenetic clocks, which analyze DNA sites undergoing hypermethylation or hypomethylation as individuals age, have paved the way for improved prediction models. A wide range of biomarkers and methods for DNA methylation analysis have been proposed, achieving different accuracies across samples and cell types. This review extensively explores literature from the past 5 years, showing scientific efforts toward the ultimate goal: applying age prediction models to assist in human identification.
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Affiliation(s)
- María Josefina Castagnola
- Department of Chemistry and Environmental Sciences, New Jersey Institute of Technology, Tiernan Hall 365, Newark, NJ 07102, USA; (M.J.C.); (F.M.-P.)
| | - Francisco Medina-Paz
- Department of Chemistry and Environmental Sciences, New Jersey Institute of Technology, Tiernan Hall 365, Newark, NJ 07102, USA; (M.J.C.); (F.M.-P.)
| | - Sara C. Zapico
- Department of Chemistry and Environmental Sciences, New Jersey Institute of Technology, Tiernan Hall 365, Newark, NJ 07102, USA; (M.J.C.); (F.M.-P.)
- Department of Anthropology and Laboratories of Analytical Biology, National Museum of Natural History, MRC 112, Smithsonian Institution, Washington, DC 20560, USA
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Qu W, Wang F, Sun D, Liu Y, Jin X, Gong Z, Liu J, Zhang N, Wen D, Wang C, Jia H, Xu R, Tang X, Chen S, Fu X, Li X, Rong H, Zhang T, Jin C, Chen L, Li J, Liu Y, Cai J, Jiang B, Zha L. Internal validation of the GA118-24B Genetic Analyzer, a stable capillary electrophoresis system for forensic DNA identification. Int J Legal Med 2024; 138:361-373. [PMID: 37843624 DOI: 10.1007/s00414-023-03106-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Accepted: 09/29/2023] [Indexed: 10/17/2023]
Abstract
The GA118-24B Genetic Analyzer (hereafter, "GA118-24B") is an independently developed capillary electrophoresis instrument. In the present research, we designed a series of validation experiments to test its performance at detecting DNA fragments compared to the Applied Biosystems 3500 Genetic Analyzer (hereafter, "3500"). Three commercially available autosomal short tandem repeat multiplex kits were used in this validation. The results showed that GA118-24B had acceptable spectral calibration for three kits. The results of accuracy and concordance studies were also satisfactory. GA118-24B showed excellent precision, with a standard deviation of less than 0.1 bp. Sensitivity and mixture studies indicated that GA118-24B could detect low-template DNA and complex mixtures as well as the results generated by 3500 in parallel experiments. Based on the experimental results, we set specific analytical and stochastic thresholds. Besides, GA118-24B showed superiority than 3500 within certain size ranges in the resolution study. Instead of conventional commercial multiplex kits, GA118-24B performed stably on a self-developed eight-dye multiplex system, which were not performed on 3500 Genetic Analyzer. We compared our validation results with those of previous research and found our results to be convincing. Overall, we conclude that GA118-24B is a stable and reliable genetic analyzer for forensic DNA identification.
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Affiliation(s)
- Weifeng Qu
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Feng Wang
- Ministry of Public Security of P.R.C., The First Research Institute, No. 1. Shouti South Road, Beijing, 100044, China
| | - Dan Sun
- Ministry of Public Security of P.R.C., The First Research Institute, No. 1. Shouti South Road, Beijing, 100044, China
| | - Yi Liu
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Xin Jin
- Public Security Department of Hainan Province, No. 9. Binya Road, Hainan, 570203, China
| | - Zheng Gong
- Criminal Technology Detachment, Public Security Bureau of Harbin, No. 35. Dongfeng Road, Harbin, 150010, China
| | - Jinjie Liu
- Criminal Investigation Detachment, Public Security Bureau of Beijing, No. 44. Banbuqiao Road, Beijing, 102611, China
| | - Ningjie Zhang
- Ministry of Public Security of P.R.C., The First Research Institute, No. 1. Shouti South Road, Beijing, 100044, China
| | - Dan Wen
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Chudong Wang
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Hongtao Jia
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Ruyi Xu
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Xuan Tang
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Siqi Chen
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Xiaoyi Fu
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Xue Li
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Haibo Rong
- Ministry of Public Security of P.R.C., The First Research Institute, No. 1. Shouti South Road, Beijing, 100044, China
| | - Tao Zhang
- Ministry of Public Security of P.R.C., The First Research Institute, No. 1. Shouti South Road, Beijing, 100044, China
| | - Chuan Jin
- Ministry of Public Security of P.R.C., The First Research Institute, No. 1. Shouti South Road, Beijing, 100044, China
| | - Li Chen
- Ministry of Public Security of P.R.C., The First Research Institute, No. 1. Shouti South Road, Beijing, 100044, China
| | - Jienan Li
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Ying Liu
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Jifeng Cai
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China
| | - Bowei Jiang
- Ministry of Public Security of P.R.C., The First Research Institute, No. 1. Shouti South Road, Beijing, 100044, China.
| | - Lagabaiyila Zha
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No. 172. Tongzipo Road, Changsha, 410013, China.
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Naue J. Getting the chronological age out of DNA: using insights of age-dependent DNA methylation for forensic DNA applications. Genes Genomics 2023; 45:1239-1261. [PMID: 37253906 PMCID: PMC10504122 DOI: 10.1007/s13258-023-01392-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Accepted: 04/15/2023] [Indexed: 06/01/2023]
Abstract
BACKGROUND DNA analysis for forensic investigations has a long tradition with important developments and optimizations since its first application. Traditionally, short tandem repeats analysis has been the most powerful method for the identification of individuals. However, in addition, epigenetic changes, i.e., DNA methylation, came into focus of forensic DNA research. Chronological age prediction is one promising application to allow for narrowing the pool of possible individuals who caused a trace, as well as to support the identification of unknown bodies and for age verification of living individuals. OBJECTIVE This review aims to provide an overview of the current knowledge, possibilities, and (current) limitations about DNA methylation-based chronological age prediction with emphasis on forensic application. METHODS The development, implementation and application of age prediction tools requires a deep understanding about the biological background, the analysis methods, the age-dependent DNA methylation markers, as well as the mathematical models for age prediction and their evaluation. Furthermore, additional influences can have an impact. Therefore, the literature was evaluated in respect to these diverse topics. CONCLUSION The numerous research efforts in recent years have led to a rapid change in our understanding of the application of DNA methylation for chronological age prediction, which is now on the way to implementation and validation. Knowledge of the various aspects leads to a better understanding and allows a more informed interpretation of DNAm quantification results, as well as the obtained results by the age prediction tools.
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Affiliation(s)
- Jana Naue
- Institute of Forensic Medicine, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
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6
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Kayser M, Branicki W, Parson W, Phillips C. Recent advances in Forensic DNA Phenotyping of appearance, ancestry and age. Forensic Sci Int Genet 2023; 65:102870. [PMID: 37084623 DOI: 10.1016/j.fsigen.2023.102870] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 04/04/2023] [Indexed: 04/09/2023]
Abstract
Forensic DNA Phenotyping (FDP) comprises the prediction of a person's externally visible characteristics regarding appearance, biogeographic ancestry and age from DNA of crime scene samples, to provide investigative leads to help find unknown perpetrators that cannot be identified with forensic STR-profiling. In recent years, FDP has advanced considerably in all of its three components, which we summarize in this review article. Appearance prediction from DNA has broadened beyond eye, hair and skin color to additionally comprise other traits such as eyebrow color, freckles, hair structure, hair loss in men, and tall stature. Biogeographic ancestry inference from DNA has progressed from continental ancestry to sub-continental ancestry detection and the resolving of co-ancestry patterns in genetically admixed individuals. Age estimation from DNA has widened beyond blood to more somatic tissues such as saliva and bones as well as new markers and tools for semen. Technological progress has allowed forensically suitable DNA technology with largely increased multiplex capacity for the simultaneous analysis of hundreds of DNA predictors with targeted massively parallel sequencing (MPS). Forensically validated MPS-based FDP tools for predicting from crime scene DNA i) several appearance traits, ii) multi-regional ancestry, iii) several appearance traits together with multi-regional ancestry, and iv) age from different tissue types, are already available. Despite recent advances that will likely increase the impact of FDP in criminal casework in the near future, moving reliable appearance, ancestry and age prediction from crime scene DNA to the level of detail and accuracy police investigators may desire, requires further intensified scientific research together with technical developments and forensic validations as well as the necessary funding.
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Affiliation(s)
- Manfred Kayser
- Department of Genetic Identification, Erasmus MC, University Medical Center Rotterdam, Rotterdam, the Netherlands.
| | - Wojciech Branicki
- Institute of Zoology and Biomedical Research, Jagiellonian University, Kraków, Poland,; Institute of Forensic Research, Kraków, Poland
| | - Walther Parson
- Institute of Legal Medicine, Medical University of Innsbruck, Innsbruck, Austria; Forensic Science Program, The Pennsylvania State University, PA, USA
| | - Christopher Phillips
- Forensic Genetics Unit, Institute of Forensic Sciences, University of Santiago de Compostela, Spain
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Jiang L, Zhang K, Wei X, Li J, Wang S, Wang Z, Zhou Y, Zha L, Luo H, Song F. Developing a male-specific age predictive model based on Y-CpGs for forensic analysis. Forensic Sci Int 2023; 343:111566. [PMID: 36640536 DOI: 10.1016/j.forsciint.2023.111566] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 12/22/2022] [Accepted: 01/09/2023] [Indexed: 01/13/2023]
Abstract
In forensic work, predicting the age of the criminal suspect or victim could provide beneficial clues for investigation. Epigenetic age estimation based on age-correlated DNA methylation has been one of the most widely studied methods of age estimation. However, almost all available epigenetic age prediction models are based on autosomal CpGs, which are only applicable to single-source DNA samples. In this study, we screened the available methylation data sets to identify loci with potential to meet the objectives of this study and then established a male-specific age prediction model based on 2 SNaPshot systems that contain 13 Y-CpGs and the mean absolute deviation (MAD) values were 4-6 years. The multiplex methylation SNaPshot systems and age-predictive model have been validated for sensitivity (the DNA input could be as low as 0.5 ng) and male specificity. They are supposed to have feasibility in forensic practice. In addition, it demonstrated that the method was also applicable to bloodstains, which were commonly found at crime scenes. The results showed good performance (the training set: R2 = 0.9341, MAD = 4.65 years; the test set: R2 = 0.8952, MAD = 5.73 years) in case investigation for predicting male age. For mixtures, when the male to female DNA ratio is 1:1, 1:10, the deviation between the actual age and the predicted age obtained by the model was less than 8 years, which offers great hope for future prediction of the age of males in mixtures and will be a powerful tool for special cases, such as sexual assault. Furthermore, the work provides a basis for the application of Y-CpGs in forensic science.
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Affiliation(s)
- Lanrui Jiang
- Department of Forensic Genetics, West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province 610041, China
| | - Ke Zhang
- Department of Forensic Genetics, West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province 610041, China; Public Security Bureau of Zhengzhou City, Zhengzhou, Henan Province 450003, China
| | - Xiaowen Wei
- Department of Forensic Genetics, West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province 610041, China
| | - Jiahang Li
- Department of Forensic Genetics, West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province 610041, China
| | - Shuangshuang Wang
- Department of Forensic Genetics, West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province 610041, China
| | - Zefei Wang
- Department of Forensic Genetics, West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province 610041, China
| | - Yuxiang Zhou
- Department of Forensic Genetics, West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province 610041, China
| | - Lagabaiyila Zha
- Department of Forensic Science, School of Basic Medical Sciences, Central South University, No172. Tongzipo Road, Changsha, Hunan Province 410013, China
| | - Haibo Luo
- Department of Forensic Genetics, West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province 610041, China.
| | - Feng Song
- Department of Forensic Genetics, West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province 610041, China.
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Hong SR, Shin KJ. Can we integrate method-specific age-predictive models?: Analysis method-induced differences in detected DNA methylation status. Forensic Sci Int Genet 2023; 62:102805. [PMID: 36379153 DOI: 10.1016/j.fsigen.2022.102805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Revised: 11/02/2022] [Accepted: 11/08/2022] [Indexed: 11/11/2022]
Abstract
Forensic research surrounding the use of DNA methylation (DNAm) markers to predict age suggests that accurate prediction of chronological age can be achieved with just several DNAm markers. Several age-prediction models are based on DNAm levels that are detectable by a diverse range of DNAm analysis methods. Among the many DNAm analysis methods, targeted amplicon-based massively parallel sequencing (MPS) and single-base extension (SBE) methods have been widely studied owing to their practicality, including their multiplex capabilities. Since these two DNAm analysis methods share an identical amplification step during their experimental processes, several studies have compared the differences between the methods to construct integrated age-prediction models based on both MPS and SBE data. In this study, we compared the specific differences in DNAm levels between these two commonly exploited analysis methods by analyzing the identical PCR amplicons from the same samples and quantifying the actual bisulfite-converted DNA amount involved in the PCR step. The DNAm levels of five well-studied age-associated markers-CpGs on the ELOVL2, FHL2, KLF14, MIR29B2CHG, and TRIM59 genes-were obtained from blood samples of 250 Koreans using both DNAm analysis methods. The results showed that only ELOVL2 is interchangeable between the MPS and SBE methods, while the rest of the markers showed significant differences in DNAm values. These differences may result in high errors and consequential lowered accuracy in age estimates. Therefore, a DNAm analysis method-specific approach that considers method-induced DNAm differences is recommended to improve the overall accuracy and reliability of age-prediction methods.
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Affiliation(s)
- Sae Rom Hong
- Department of Forensic Medicine, Graduate School of Medical Science, Brain Korea 21 Project, Yonsei University College of Medicine, 50-1 Yonsei-ro, 03722 Seoul, Republic of Korea
| | - Kyoung-Jin Shin
- Department of Forensic Medicine, Graduate School of Medical Science, Brain Korea 21 Project, Yonsei University College of Medicine, 50-1 Yonsei-ro, 03722 Seoul, Republic of Korea.
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A collaborative exercise on DNA methylation-based age prediction and body fluid typing. Forensic Sci Int Genet 2021; 57:102656. [PMID: 34973557 DOI: 10.1016/j.fsigen.2021.102656] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 12/09/2021] [Accepted: 12/14/2021] [Indexed: 11/20/2022]
Abstract
DNA methylation has become one of the most useful biomarkers for age prediction and body fluid identification in the forensic field. Therefore, several assays have been developed to detect age-associated and body fluid-specific DNA methylation changes. Among the many methods developed, SNaPshot-based assays should be particularly useful in forensic laboratories, as they permit multiplex analysis and use the same capillary electrophoresis instrumentation as STR analysis. However, technical validation of any developed assays is crucial for their proper integration into routine forensic workflow. In the present collaborative exercise, two SNaPshot multiplex assays for age prediction and a SNaPshot multiplex for body fluid identification were tested in twelve laboratories. The experimental set-up of the exercise was designed to reflect the entire workflow of SNaPshot-based methylation analysis and involved four increasingly complex tasks designed to detect potential factors influencing methylation measurements. The results of body fluid identification from each laboratory provided sufficient information to determine appropriate age prediction methods in subsequent analysis. In age prediction, systematic measurement differences resulting from the type of genetic analyzer used were identified as the biggest cause of DNA methylation variation between laboratories. Also, the use of a buffer that ensures a high ratio of specific to non-specific primer binding resulted in changes in DNA methylation measurement, especially when using degenerate primers in the PCR reaction. In addition, high input volumes of bisulfite-converted DNA often caused PCR failure, presumably due to carry-over of PCR inhibitors from the bisulfite conversion reaction. The proficiency of the analysts and experimental conditions for efficient SNaPshot reactions were also important for consistent DNA methylation measurement. Several bisulfite conversion kits were used for this study, but differences resulting from the use of any specific kit were not clearly discerned. Even when different experimental settings were used in each laboratory, a positive outcome of the study was a mean absolute age prediction error amongst participant's data of only 2.7 years for semen, 5.0 years for blood and 3.8 years for saliva.
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