Influence of an individual's age on the amount and interpretability of DNA left on touched items

Abstract

In crime scene investigations, DNA left by touch on an object can be found frequently and the significant improvements in short tandem repeat (STR) amplification in recent years built up a high expectation to identify the individual(s) who touched the object by their DNA profile. Nevertheless, the percentage of reliably analysable samples varies considerably between different crime scenes even if the nature of the stains appears to be very similar. Here, it has been proposed that the amount and quality of DNA left at a crime scene may be influenced by external factors (like nature of the surface) and/or individual factors (like skin conditions). In this study, the influence of the age of an individual who left his DNA on an object is investigated. Handprints from 213 individuals (1 to 89 years old) left on a plastic syringe were analysed for DNA amount and STR alleles using Quantifiler® and PowerPlex® ESX 17. A full profile of the individual could be found in 75 % of all children up to 10 years, 9 % of adolescents (11 to 20 years), 25 % of adults (21 to 60 years) and 8 % of elderly people (older than 60 years). No person older than 80 years displayed a full profile. Drop-in and drop-out artefacts occurred frequently throughout the age groups. A dependency of quantity and quality of the DNA left on a touched object on the age of the individual could be clearly demonstrated at least for children and elderly people. An epithelial abrasion unexpectedly good to interpret may be derived from a child, whereas the suspected skin contact of an elderly person with an object may be impossible to prove.

A molecular exploration of human DNA/RNA co-extracted from the palmar surface of the hands and fingers

“…No variables other than gender could be clearly identified by the LCA as being associated with individuals who had a stronger probability to carry high amounts of DNA on their hands, with the partial exception of the absence of a tendency to touch or to play with hair. In particular, no clear subdivision was found in relation to age, which has recently been described as a factor that may possibly influence the extent of DNA transfer [40].…”

A review of trace “Touch DNA” deposits: Variability factors and an exploration of cellular composition

“…Some authors have reported increased DNA "shedding" or "sloughing" in men versus women [44], and in young males compared to older ones (the same trend was not observed in females), but significantly, over ¾ of subjects changed status (good/ intermediate/ poor) between trials three days apart [45]. Others concluded that while children are typically "better" shedders and the elderly somewhat "worse," adults in the categories in between are significantly less predictable [46]. Although high intra-and inter-individual variation is consistently reported [47,48], many authors report that those subjects whose handled items yield either more or better quality DNA are a quantifiable group [44,47,49,50].…”

DNA transfer in forensic science: A review

“…Skin conditions that increase the proliferation rate of the skin cells, such as dermatitis and psoriasis, may also result in the deposition of higher quantities of DNA through touch [116]. Further, studies have shown that younger individuals tend to deposit greater quantities of DNA compared to those that are older [117,118], while males may be more likely to be classified as heavy shedders compared to females [105,117,119]. Determining the extent to which genetic factors and various non-genetic factors (e.g.…”