The prevalence of mixed DNA profiles in fingernail samples taken from individuals in the general population

Forensic Genetics and Genotyping

“…The persistence of foreign DNA under the nails generally lasts up to 6 h (8). Cook and Dixon in their study detected foreign DNA in 13% of samples after 24 h (21).…”

“…The fingernail hyponychium can provide a valuable source of evidential material for investigation (8,21). Traces of skin (especially if the victim scratched the perpetrator), body fluids and hairs may collect under the nails.…”

Avoiding Errors and Pitfalls in Evidence Sampling for Forensic Genetics

“…Rutty and Graham (2005) described airborne DNA contamination in mortuaries. Methods were described in order to avoid the possibility of contaminations:  To perform analyses about the persistence of DNA on different kinds of surfaces in various environmental conditions (Toothman et al, 2008;Rutty et al, 2003;Cook et Dixon, 2007);  To improve and standardize the sample collection methodologies in order to improve the targeting of the samples and to decrease unwanted underlying DNA;  To collect the profiles of all the persons involved in the collecting and laboratory steps to recognize a contamination coming from these professionals;  Some laboratories require samples from the area immediately adjacent to the target area to have a so called "blank sample". The operating procedures on the crime scene must be precisely fixed to minimize the possibility of contaminations (Rutty et al, 2003):  To avoid breathing, talking and of course coughing during the sampling step in restricting the access of non specialist investigators to the scene;  The use full-body scene suit (to avoid contamination by cell shedding coming from exposed areas of skin), hood, hair net, gloves and mouth masks by all the investigators in charge of the sampling step;  To avoid direct touching of the evidences containing the DNA and changing gloves and masks regularly at the crime scene and obviously in the laboratories;  All the results are compared against the database containing the DNA profiles of all the persons who were involved in all the steps of the sampling and laboratory processing of the evidences in order to detect contaminations coming from them;  To use DNA-free disposable equipment to collect the DNA on the target surfaces (Van Oorschot et al, 2005), and to systematically decontaminate thoroughly all the devices which would be in physical contact with the sample.…”

Systematic analysis of decadactylar subungueal genetic traces in murder cases

“…This exogenous profile can be matched with a potential suspect, or through a DNA database search. The importance of these finding increases if it is considered that, even though casual physical activities may leave traces of biological material under the fingernails, the background level of this cellular debris is not usually sufficient to produce detectable DNA mixtures as several studies have been demonstrated [3][4][5]. Therefore, it is mandatory to follow a careful protocol involving sampling and DNA extraction to optimize results as it is described in the literature [6,7].…”