Changes over time in genetic profiles obtained from saliva deposited on clothing

TRABAJO LIBRE SOMETIDO AL III CONGRESO DE CIENCIAS FORENSES DE HONDURAS DEL 8 AL 10 DE OCTUBRE, TEGUCIGALPA, HONDURAS

Abstract

Objective: To analyze the usefulness of genetic profiles obtained from DNA on saliva-stained clothing in a sexual crime scenario.
Introduction: Forensic genetic analysis is a key tool for identifying individuals in criminal investigations, particularly in sexual offenses, where biological evidence plays a fundamental role (1). Saliva constitutes one of the main biological evidence in cases of sexual assault (2). Its analysis allows obtaining genetic profiles useful for identifying aggressors, because it contains epithelial cells detached from the oral mucosa (3). However, this fluid has limitations associated with its enzymatic composition and the action of nucleases, which can accelerate DNA degradation under environmental conditions (4). Therefore, it is essential to know the durability and quality of DNA obtained from saliva deposited on clothing over time.
Methodology: Saliva samples were collected from one female and one male volunteer, with informed consent. Saliva samples (50 µL, equivalent to one drop) were deposited separately on 100% cotton T-shirts. Each T-shirt was divided into spaces, which were assigned for each month of analysis (T0–T6). The fabric fragments were processed at the beginning of the study (T0) and subsequently processed monthly for 6 months (T2–T6). DNA extraction was performed using the commercial PrepFiler Express BTA™ kit. The samples were then quantified by real-time PCR with the Quantifiler HP kit, evaluating the concentration and degradation index (DI) of DNA. Amplification was carried out with the GlobalFiler™ kit, and amplicon separation was performed with the ABI PRISM® 3500 analyzer to obtain genetic profiles.
Results: DNA concentrations showed considerable variability over time, with values ​​ranging from 0.11 and 49.73 ng/µL. Furthermore, the analyzed samples exhibited DNA degradation, with ID values ​​ranging from 0.64 and 2.38 (Table 1). However, this degradation did not compromise the acquisition of complete genetic profiles. Electropherograms revealed a decrease in signal intensity at time T6 compared to T0, with no loss of alleles or the appearance of relevant artifacts. Therefore, complete genetic profiles useful for forensic identification were obtained over the course of six months.
Discussion and conclusions: Saliva deposited on clothing can contain DNA in sufficient quantity and quality to obtain complete genetic profiles for at least six months after deposit, under controlled storage conditions. Although variations in DNA concentration and degradation were observed, the integrity of the genetic profiles was maintained. These results confirm that genetic profiles obtained from DNA from saliva-stained clothing could be useful in the investigation of certain specific types of sexual offenses.