Rhonda K. Roby, MPH, Theodore D. Anderson, MFS, James P. Ross, BS, Demris A. Lee, MSFS, Mitchell M. Holland, PhD and Victor W. Weedn, LTC, MC, USA
Department of Defense DNA Registry, Office of the Armed Forces Medical Examiner, Armed Forces
Institute of Pathology, Rockville, MD

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Collection of trace evidence underneath a victim’s fingernails is part of a routine autopsy examination; yet the collection of fingernails at a crime scene is not so common. Forensic examinations of nail evidence include striation and tear comparisons and deoxyribonucleic acid (DNA) analysis. To date, the Department of Defense DNA Registry has been requested to process nails from two different cases. A review of the cases will be presented.

In order to process nails as evidence, a validation study was performed to demonstrate that DNA could be successfully extracted from human nail material. Organic extractions of DNA were performed on fresh fingernails, fresh toenails, and aged (~eight years old) fingernails. The isolated DNA was quantified and analyzed by polymerase chain reaction (PCR)-based testing. This study demonstrated that the extraction of fresh, human nail material yielded sufficient quantities of DNA for successful short tandem repeat (STR) analysis and mitochondrial DNA (mtDNA) sequencing. A random sampling of fingernails from 22 different individuals (15 females, 6 males and 1 unknown) was tested. Successful STR profiles were obtained from all fingernail specimens collected from male individuals. Full or partial STR profiles were obtained from the fingernail specimens collected from 10 of the 15 female individuals. All nails amplified for mtDNA produced PCR product; all products sequenced produced the correct mtDNA type. Organic extraction of aged human nail material yielded a sufficient quantity of DNA for successful mtDNA sequencing; however, STR analysis was unsuccessful.

Furthermore, this study involved the development of a cleaning procedure designed to remove both physical (i.e. gold-palladium) and biological (i.e. whole blood) surface contaminants. Several cleaning procedures were attempted on small fragments of human fingernails which were contaminated by immersion in whole blood, bare-handed manipulation, gold-palladium coating, or a combination of immersion in whole blood and gold-palladium coating. These procedures included vortexing, ultrasonication, immersion in water, ethanol, acetone, sodium dodecyl sulfate (SDS) and/or bleach, double-extraction, or a combination of these procedures. The use of bleach, in conjunction with some method of agitation, was observed to be an effective cleaning agent and did not adversely affect the extraction, amplification or analysis of the DNA from human nail material.

Certain cleaning methods were considered unsuccessful based on the presence of mixtures in STR profiles. However, all cleaning methods yielded a single correct mtDNA sequence. This led to an investigation of the amount of contaminating DNA necessary to result in the presence of a mixture in a mtDNA sequence. The conclusion was drawn that, when extracting approximately 2.5 mg of human nail material, several microliters of whole blood had to be added directly to the extraction buffer in order to produce a mixture in the mtDNA sequence.

This validation study will provide a foundation for future use of forensic, PCR-based DNA testing to obtain a DNA profile from evidentiary nails which may contain surface contaminates.