DNA Extraction From Archived Slides: Analysis and Use in Current Forensic Identification

Positive identification of human remains in missing persons cases can be difficult, especially when dental records or other information normally utilized are not available. Pap smears and other paraffin-embedded tissues taken and archived by medical professionals are a potential resource in the identification of remains in such cases. However, before this material can be useful to forensic scientists, an efficient DNA isolation and analysis protocol must be developed and properly validated. The protocol must work satisfactorily with fresh, archived, and possibly degraded samples when using the multiplexed short tandem repeat (STR) systems, the current standard in DNA identification. We have developed a protocol for the efficient removal of the coverslip from the slide, destaining, DNA extraction, and DNA quantification. DNA recovered by this protocol was amplified with the Profiler Plus and COfiler multiplex primer sets (Applied Biosystems), and analyzed by capillary electrophoresis. 55 Pap smear samples were tested, which ranged in age from 2 weeks to more than 6 years. The revised protocol reduces by several days the time required by other methods for coverslip removal. In addition, destaining was improved, which increased the number of genetic loci that could be typed. Although some allele dropout was observed in the older samples, all of the samples tested gave results which would identify the origin of the samples to between 1 in 10³ and 1 in 10¹⁹individuals. This technique combines efficiency with availability, and demonstrates that DNA isolated from archived Pap smears can continue to be a useful tool in forensic cases.