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.
Highlights
Human genetic variation—in particular, the use of short tandem repeat (STR) markers—allows for individual identification of known persons, such as donors of biological traces found at crime scenes [1,2]
While DNA methylation occurs in the 50 carbon of cytosine in 50 -CpG-30 positions without affecting the DNA sequence itself, such epigenetic differences can be detected with both genome-wide screening and targeted methods
Based on observations derived from genome-wide data, potential candidate markers capable of discriminating identical twins have been reported in blood [24,25] and buccal cells [12]; studies on testing the forensic feasibility and applicability of this are lacking
Summary
Human genetic variation—in particular, the use of short tandem repeat (STR) markers—allows for individual identification of known persons, such as donors of biological traces found at crime scenes [1,2]. A complete match between an STR profile from a crime scene trace and that of a known person indicates that the matching person is the trace donor. Except for extremely rare cases [3], such conventional forensic DNA profiling fails to discriminate monozygotic (MZ) twins from within a given pair, which can be forensically. Genes 2018, 9, 252 relevant in both criminal and paternity casework. This challenge is due to the fact that MZ twins from the same pair derive from the same zygote, sharing an ‘identical’ genome sequence and the same forensic STR profile. A suitable molecular approach needs to be developed to differentiate MZ twins from crime scene stains to be able to solve such criminal cases
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
