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Genes 2018, 9(5), 252; https://doi.org/10.3390/genes9050252

Investigating the Epigenetic Discrimination of Identical Twins Using Buccal Swabs, Saliva, and Cigarette Butts in the Forensic Setting

1
Department of Genetic Identification, Erasmus MC University Medical Center Rotterdam, 3015 CN Rotterdam, The Netherlands
2
Department of Twin Research and Genetic Epidemiology, King’s College London, London SE1 7EH, UK
Current address: Pfizer-University of Granada-Andalusian Government Center for Genomics and Oncological Research (GENYO), 18007 Granada, Spain.
*
Author to whom correspondence should be addressed.
Received: 30 March 2018 / Revised: 7 May 2018 / Accepted: 7 May 2018 / Published: 14 May 2018
(This article belongs to the Special Issue Forensic Genomics)
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Abstract

Monozygotic (MZ) twins are typically indistinguishable via forensic DNA profiling. Recently, we demonstrated that epigenetic differentiation of MZ twins is feasible; however, proportions of twin differentially methylated CpG sites (tDMSs) identified in reference-type blood DNA were not replicated in trace-type blood DNA. Here we investigated buccal swabs as typical forensic reference material, and saliva and cigarette butts as commonly encountered forensic trace materials. As an analog to a forensic case, we analyzed one MZ twin pair. Epigenome-wide microarray analysis in reference-type buccal DNA revealed 25 candidate tDMSs with >0.5 twin-to-twin differences. MethyLight quantitative PCR (qPCR) of 22 selected tDMSs in trace-type DNA revealed in saliva DNA that six tDMSs (27.3%) had >0.1 twin-to-twin differences, seven (31.8%) had smaller (<0.1) but robustly detected differences, whereas for nine (40.9%) the differences were in the opposite direction relative to the microarray data; for cigarette butt DNA, results were 50%, 22.7%, and 27.3%, respectively. The discrepancies between reference-type and trace-type DNA outcomes can be explained by cell composition differences, method-to-method variation, and other technical reasons including bisulfite conversion inefficiency. Our study highlights the importance of the DNA source and that careful characterization of biological and technical effects is needed before epigenetic MZ twin differentiation is applicable in forensic casework. View Full-Text
Keywords: forensics; epigenomics; individual identification; monozygotic twins; DNA methylation; Illumina 450K array; MethyLight; buccal cells; saliva; cigarette butts forensics; epigenomics; individual identification; monozygotic twins; DNA methylation; Illumina 450K array; MethyLight; buccal cells; saliva; cigarette butts
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Vidaki, A.; Kalamara, V.; Carnero-Montoro, E.; Spector, T.D.; Bell, J.T.; Kayser, M. Investigating the Epigenetic Discrimination of Identical Twins Using Buccal Swabs, Saliva, and Cigarette Butts in the Forensic Setting. Genes 2018, 9, 252.

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