Shedder status: Does it really exist?

Shedder status: Does it really exist?

Forensic Science International: Genetics Supplement Series 7 (2019) 360–362 Contents lists available at ScienceDirect Forensic Science International...

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Forensic Science International: Genetics Supplement Series 7 (2019) 360–362

Contents lists available at ScienceDirect

Forensic Science International: Genetics Supplement Series journal homepage:

Shedder status: Does it really exist? Jiayu Tan⁎, Jun Yu Lee, Li Yen Candy Lee, Zhen Qin Aw, Mee Hui Chew, Nurul Insyirah Binte Ishak, Yong Sheng Lee, Marlene Abdul Mugni, Christopher Kiu Choong Syn


DNA Profiling Laboratory, Biology Division, Health Sciences Authority, 3 Biopolis Drive, 138623, Singapore



Keywords: Touch DNA DNA transfer Activity

The concept of shedder status is not new, and studies have been conducted by multiple groups but with varying results. Hence, to investigate the validity of the shedder status concept, a total of 486 touch DNA samples were collected from 81 individuals to examine DNA recovery 15 min post-handwashing. We defined the shedder status of participants using the dual requirement of number of self-alleles detected and the frequency of occurrence. While some participants had consistently high or low allele deposition, other participants showed great intraperson variation. Significant differences in the number of self-alleles were also observed between genders, and for the activities of self-contact and mobile phone usage.

1. Introduction

2.2. DNA processing

The ability to generate DNA profiles from touched items has brought about great reliance on touch DNA in criminal investigations today. One frequently discussed factor affecting the deposition of touch DNA is shedder status. While studies on shedder status have been numerous, the findings were inconsistent [1–7]. Our study sought to address the question of whether the concept of shedder status is valid by examining DNA recovery 15 min post-handwashing from 81 individuals. Information on participants’ personal details and activities were collected through a questionnaire, to investigate if any variables are associated with one’s shedder status.

DNA extraction was performed on the swabs using the DNA IQ™ Casework Extraction Kit for pre-processing and DNA IQ™ Casework Pro Kit for extraction on Maxwell® FSC instrument (Promega, USA). DNA yield was estimated using Quantifiler® Duo DNA Quantification kit (Applied Biosystems) on QuantStudio™ 7 Flex Real-Time PCR System (Applied Biosystems). DNA extract was amplified (29 cycles) with GlobalFiler™ kit (Applied Biosystems) with maximum of 15 μL or 1 ng input DNA. Capillary electrophoresis was performed on ABI PRISM® 3500xL Genetic Analyzer (Applied Biosystems) with maximum injection parameters of 3 μL at 1.2 kV 24 s. Results were analyzed using GeneMapper® ID-X v1.2 software according to laboratory guidelines.

2. Materials and methods 2.1. Experimental design Eighty-one participants washed their hands thoroughly with soap and water, then dabbed dry with clean paper towels. They resumed normal activities for 15 min with instructions to avoid food consumption, wear gloves or touch another person. Thereafter, participants gripped a DNA-free 50 mL plastic tube in each hand for 10 s. DNA deposited on the tubes were collected with sterile cotton swabs. Participants then completed a questionnaire detailing the items they had touched during the 15 min. This process was repeated on another two days within a week, giving a total of 486 samples.

Corresponding author. E-mail address: [email protected] (J. Tan). Received 12 September 2019; Accepted 2 October 2019 Available online 03 October 2019 1875-1768/ © 2019 Elsevier B.V. All rights reserved.

2.3. Statistical analyses Analyses were performed using IBM SPSS statistics ver. 18. Pvalue < .05 was considered statistically significant. 3. Results 3.1. Categorisation of participants by shedder status A total of six DNA samples were collected from each participant across three days. A participant was considered a good shedder when the majority of samples (≥ 4 out of 6) gave reportable DNA profiles (i.e. minimum of 16 detected alleles). A participant was considered a poor shedder if all six profiles were not reportable. Participants with

Forensic Science International: Genetics Supplement Series 7 (2019) 360–362

J. Tan, et al.

Fig. 1. Self-alleles recovered from the 81 participants. Each participant had gripped a tube in their left and right hands, on three separate occasions, making a total of six samples per participant. Each point on the graph represents the number of self-alleles recovered in that sample. Higher intensity markers indicate overlapping data points.

4. Discussion

one to three reportable profiles were considered intermediate shedders. Only alleles matching those in the reference DNA profile of the participant were taken into consideration. Using the criteria described, the distribution of participants’ shedder status was 11% good, 41% intermediate and 48% poor.

Notably, 1% of samples had entirely foreign alleles. This finding is in agreement with Goray et al. [6] who reported that it was possible to transfer foreign DNA without any self-DNA in almost 3% of their samples (7 out of 240), contradicting the study by Manoli et al. [4] where the participant’s DNA is always present, as well as the study by Phipps and Petricevic which reported negligible secondary transfer [2]. The contributors of the foreign alleles in our study could all be attributed to co-workers of the respective participants, indicating that DNA transfer in the work setting would be the most probable explanation. Next, we investigated if shedder status was associated with any personal traits or behavioural factors. In agreement with several published studies [4–7], we observed that males are more often categorised as good shedders than females. Conflicting data has been published regarding the association of shedder status with hand dominance [2,4,6] and our results suggested no such association. Our study also suggested no association between age and shedder status whereas Manoli et al. [4] found an association in male participants. Importantly, our study found a significant difference in the number of self-alleles detected with two specific activities: (1) self-contact and (2) usage of personal mobile phone. These findings suggest that shedder status is greatly influenced by one’s activities and habits. By not limiting participants’ activity during the 15 min interval between handwashing and handling of the tube, we would be categorising the participants based on both transferred self-DNA and innate propensity of skin cell shedding; instead of innate propensity of skin cell shedding alone. In conclusion, while the results of this study suggest that some individuals can indeed be classified as either good or poor shedders, being consistent in their deposition of high or low levels of DNA, respectively, a substantial number of participants in this study were inconsistent in their DNA deposition. Further studies have been initiated to shed light on an individual’s innate propensity to shed DNA, as well as the influence of different activities on DNA deposition.

3.2. DNA profiles recovered showed great inter- and intra-person variation The number of self-alleles detected from the six DNA profiles generated for each participant is shown in Fig. 1. Some participants consistently deposited very low amounts of DNA, e.g., participants 3 and 21 had zero alleles in all six of their profiles. In contrast, other participants such as participants 59 and 64 consistently deposited high levels of DNA, e.g., more than 80% of their DNA profiles could be detected in each of their six profiles. Most participants, however, were like participants 11 and 52, who showed wide variation in the number of alleles recovered from their samples. 3.3. Primary and secondary DNA transfer Of the 486 samples collected, 27% had DNA profiles with zero allele while 78% of the profiles were not reportable. In the short 15 min interval between handwashing and handling of the tubes, participants had accumulated foreign alleles in 22% of the samples although the majority (102 out of 109 samples) of these samples had low foreign allele count, below the laboratory’s reporting criteria. Interestingly, five out of 486 samples (1%) had entirely foreign DNA profiles, with no trace of participant’s self-alleles. 3.4. Statistical analyses Using the Mann-Whitney U test, there were significant differences when comparing the number of self-alleles detected in (1) male vs female participants (P < .001); (2) participants who touched part of their body vs participants who did not (P < .001); and (3) participants who used their mobile phones vs participants who did not (P < .001). No significant difference was found in the number of self-alleles when comparing left vs right hand; and dominant vs non-dominant hand. Furthermore, using the Spearman rank correlation test, the number of self-alleles was found to have no association with age of participants and the number of items touched.

Declaration of Competing Interest None. References [1] A. Lowe, C. Murray, J. Whitaker, et al., The propensity of individuals to deposit DNA


Forensic Science International: Genetics Supplement Series 7 (2019) 360–362

J. Tan, et al. and secondary transfer of low level DNA from individuals to inert surfaces, Forensic Sci. Int. 129 (2002) 25–34. [2] M. Phipps, S. Petricevic, The tendency of individuals to transfer DNA to handled items, Forensic Sci. Int. 168 (2007) 162–168. [3] D.J. Daly, C. Murphy, S.D. McDermott, The transfer of touch DNA from hands to glass, fabric and wood, Forensic Sci. Int. Genet. 6 (2012) 41–46. [4] P. Manoli, A. Antoniou, E. Bashiardes, et al., Sex-specific age association with primary DNA transfer, Int. J. Legal Med. 130 (2016) 103–112.

[5] A.E. Fonneløp, M. Ramse, T. Egeland, et al., The implications of shedder status and background DNA on direct and secondary transfer in an attack scenario, Forensic Sci. Int. Genet. 29 (2017) 48–60. [6] M. Goray, S. Fowler, B. Szkuta, et al., Shedder status – an analysis of self and non-self DNA in multiple handprints deposited by the same individuals over time, Forensic Sci. Int. Genet. 23 (2016) 190–196. [7] P. Kanokwongnuwut, B. Martin, K.P. Kirkbride, et al., Shedding light on shedders, Forensic Sci. Int. Genet. 36 (2018) 20–25.