Identification of skin in touch/contact forensic samples by messenger RNA profiling

Abstract

The true nature of touch DNA evidence has remained elusive, generally perceived to be the result of DNA obtained from shed skin cells yet never confirmed with scientific certitude. This is largely due to the belief that it is not possible to ascertain the tissue source of origin of the biological material in touch DNA evidence. Thus far, research has failed to provide crime laboratories with feasible methods to identify the tissue source of origin of touch DNA. The aim of the current work was to identify highly sensitive and specific biomarkers for the identification of skin. We have previously demonstrated the use of tissue specific messenger RNA (mRNA) profiling assays for body fluid identification. We therefore utilized mRNA profiling to identify potential biomarkers for the identification of skin. From an evaluation of over 100 potential genes, we identified five mRNA markers that demonstrated a high degree of specificity for skin. Using these markers, we have been able to successfully identify skin using as little as 5–25 pg of input RNA. The presence of skin has been successfully identified in swabs of human skin and in a variety of touch samples. One of the markers (LCE1C) is particularly highly sensitive and permits the detection of skin in a majority of known skin containing samples tested. Although further work is needed to produce an assay for routine casework, these initial studies demonstrate that a molecular-based characterization of the biological material recovered from touch samples is possible.