An Evaluation of the Relevance of Routine DNA Typing of Fingernail Clippings for Forensic Casework

Abstract

DNA extracted from fingernail clipping of victims in forensic cases is a possible source of DNA from the perpetrator in cases where victims struggled or defended themselves. The source of this DNA on a victim's fingernails could possibly originate from contact with the suspect's blood, saliva, semen or scratched skin. In this technical note we evaluate the relevance of routine 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 from a number of volunteers, before and after aggressively scratching other volunteers. No blood was drawn from the scratching, but skin flakes were observed under the nails before cutting and subsequent DNA typing. The DNA extracted was then typed using the STR systems: HUMTHO1, HUMTPOX and HUMCSF1PO (CTT triplex) and the system of D1S80. These profiles were compared with profiles achieved by similar typing of buccal swabs as a reference from each volunteer. In this study, the profile detected from each volunteer's clippings was the same before and after scratching, and matched the profile of the corresponding volunteer as defined by typing each volunteer's reference buccal swab. Fingernail clippings that are sent to our lab in actual casework are usually so small that additional treatment by swabbing or removing debris from below the clipping is not possible. For this reason, in this simulation 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 themselves, we suggest that typing of fingernail clippings should be carried out in forensic cases only when relevant. We would suggest that fingernail clippings not be routinely sent to the biology laboratory as items of evidence to be tested.

The nail and hair in forensic science

“…9 Fingernail clippings of victims have been utilized in looking for the DNA of aggressors in cases where the victims struggled to defend themselves. 10 The identification, however, may be difficult due to the fact that the aggressor's DNA is often too low in quantity to be detected. Polymerase chain reaction typing of the simple tandem repeat locus residing on the Y chromosome may allow genetic characterization in case of a male aggressor of a female victim.…”

Tests Used to Analyze Forensic Evidence in Cases of Child Sexual Abuse and Assault

“…[25][26][27] Epithelial cells can also be transferred through physical contact, providing another potential source of DNA for analysis. This material is often collected as part of the sexual assault forensic evidence kit by scraping under the nails, swabbing under the nails, or clipping the nails.…”

Obtención de ácido desoxirribonucleico (ADN) útil para análisis genético, a partir de uñas recortadas.

“…Son especialmente útiles en casos en lo que se ha realizado transplante alogénico de médula ósea, y se necesita identificar el origen de las células hematopoyéticas posttransplante, y donde debido al reemplazo de las células sanguíneas, debe obtenerse ADN de muestras distintas a la sangre periférica (5). Es también de invalorable utilidad en casos de medicina forense, donde el material de evidencia, y única fuente de ADN son uñas (6).…”