Comparison of Cervical Os Versus Vaginal Evidentiary Findings During Sexual Assault Exam

Forensic Spermatozoa Detection

Semen is crucial evidence for some sex crimes, with its sole confirmation being sperm detection. The success of sperm detection is dependent on all levels of preanalytic and analytic procedures. Specimen collection must be performed by well-trained and competent forensic physicians as well as forensic nurses, with preservation done properly before laboratory transfer. Laboratory procedures should consider archival sperm identification, by visualization, with adequate amounts separated from other cells to obtain male DNA profiles. Differential extraction is robust and accepted as the forensic standard but is time consuming and may result in male DNA loss. Thus, alternative methods and microdevices have been developed. Challenges in sperm isolation from vaginal or buccal epithelium mixes and discrimination in multiperpetrator cases have been overcome by single-cell profiling; however, problems inherent in identical twin discrimination and azoospermia have yet to be solved. Epigenetics and future molecular biomarkers may hold the key; therefore, all laboratory processes must consider DNA and RNA protection. Long-term specimen preservation should be done when possible in light of future confirmatory tests.

A Y-short tandem repeat specific DNA enhancement strategy to aid the analysis of late reported (≥ 6 days) sexual assault cases

The ability to obtain an autosomal short tandem repeat (STR) profile of the semen donor from the reproductive tract of a living victim rapidly diminishes as the post-coital interval increases. This is of concern where victims of sexual assault provide vaginal samples several days after the incident. In order to overcome the technological impediments inherent in autosomal DNA typing with extended interval samples, we previously employed the use of Y chromosome STR profiling which, by targeting only male DNA, can eliminate masking of the male profile (by the victim's alleles) or critical polymerase chain reaction reagent titration (due to excessive female DNA). Thus employing Y-STR profiling and additional enhancement strategies, we reported the ability to recover Y-STR profiles from samples collected 5 to 6 days after intercourse. However, the reproductive biology literature indicates that spermatozoa are found in the human cervix up to 7 to 10 days post coitus. Thus, even with improved extraction and profiling techniques, we failed to routinely recover profiles from samples collected ≥ 6 days after intercourse. The aim of the present work was to develop additional strategies to permit the recovery of male donor DNA profiles from ≥ 6 post-coital samples. Using nested polymerase chain reaction and DNA concentration procedures that together maximize the recovery and targeting of male DNA, we demonstrate the ability to obtain semen donor Y-STR profiles in extended interval post-coital samples collected 6 to 9 days after intercourse. This approaches the recognized time limits of sperm residence in the cervico-vaginal canal as described in the clinical literature.