Y-STR profiling in extended interval (> or = 3 days) postcoital cervicovaginal samples

Area of Science:

• Forensic Science
• Genetics
• Molecular Biology

Background:

• Sexual assault cases often involve delayed reporting, complicating evidence collection.
• Vaginal samples collected >36-48 hours post-incident present challenges for DNA profiling.

Purpose of the Study:

• To evaluate the efficacy of commercial and in-house Y-STR (Y-chromosome Short Tandem Repeat) systems for DNA profiling.
• To determine the feasibility of obtaining DNA profiles from extended-interval (> or =3 days) postcoital cervicovaginal samples.

Main Methods:

• Tested commercial Y-STR kits (AmpFlSTR Yfiler, PowerPlex Y, Y-PLEX 12) and in-house systems (MPI, MPB).
• Collected cervicovaginal swabs from three women at 3-7 days post-intercourse, ensuring 7-day abstinence prior to each act.
• Employed DNA profile enhancement techniques: cervical brushing, nondifferential DNA extraction, and post-PCR purification.

Main Results:

• Full Y-STR profiles were routinely obtained from samples collected 3-4 days post-intercourse.
• Partial profiles were achievable 5-6 days postcoitus, with full profiles less common.
• Differential lysis yielded superior DNA profiles compared to nondifferential methods.
• Post-PCR purification significantly enhanced Y-STR profile recovery, especially for 5-6 day samples.
• An 8-locus Y-STR profile was obtained from a 7-day postcoital sample.

Conclusions:

• Y-STR analysis is effective for profiling extended-interval postcoital samples in sexual assault investigations.
• Advanced DNA profiling strategies, including specific Y-STR kits and purification methods, extend the window for forensic evidence recovery.
• These findings have significant implications for sexual assault case investigations involving delayed evidence submission.