An evaluation of the relevance of routine DNA typing of fingernail clippings for forensic casework

DNA extracted from fingernail clippings of victims in forensic cases is a p ossible source of DNA from the perpetrator in cases where victims struggled or defended themselves. The source of this DNA on a victim's fingernails c ould possibly originate from contact with the suspect's blood, saliva, seme n or scratched skin. In this technical note we evaluate the relevance of ro utine DNA typing of fingernail clippings in the forensic biology laboratory when, in real casework, normally only small quantities of nail material is sent. This was carried out by extracting DNA from fingernail clippings fro m a number of volunteers, before and after aggressively scratching other vo lunteers. No blood was drawn from the scratching, but skin flakes were obse rved under the nails before cutting and subsequent DNA. typing. The DNA ext racted was then typed using the STR systems: HUMTHO1, HUMTPOX and HUMCSF1PO (CTT tripler) and the system of D1S80. These profiles were compared with p rofiles achieved by similar typing of buccal swabs as a reference from each volunteer. In this study, the profile detected from each volunteer's clipp ings was the same before and after scratching, and matched the profile of t he corresponding volunteer as defined by typing each volunteer's reference buccal swab. Fingernail clippings that are sent to our lab in actual casewo rk are usually so small that additional treatment by swabbing or removing d ebris from below the clipping is not possible. For this reason, in this sim ulation the entire clippings were used for DNA extraction, to maximize the possibility of finding an additional profile. In conclusion, the findings from this study show that although the profiles obtained when typing fingernail clippings are those of the donors themselv es, we suggest that typing of fingernail clippings should be carried out in forensic cases only when relevant. We would suggest that fingernail clippi ngs not be routinely sent to the biology laboratory as items of evidence to be tested.