Improving the Quality of Compromised DNA Evidence

A new publication made available through the National Criminal Justice Reference Service by NIJ focuses on the development of a method that would physically repair double strand breaks in damaged (or degraded) DNA.

From the abstract of "Tools for Improving the Quality of Aged, Degraded, Damaged, or Otherwise Compromised DNA Evidence" by Michael M. Cox, Ph.D. and Evelyn M. Mercer:

DNA samples collected from the scenes of crimes or disasters can often be too degraded for standard forensic analytical procedures due to DNA double strand breaks. Many law enforcement agencies also possess archived crime scene evidence from cold cases that are decades old in which the DNA has become too damaged to analyze because of DNA double strand breaks. The purpose of this study is to develop a new method to repair double strand breaks in forensic DNA samples as a pretreatment for the standard short tandem repeat (STR) analysis protocols.
The authors were able to develop reproducible procedures for the artificial degradation of human DNA samples using ionizing radiation to inflict a DNA damage profile that reprises that of a typical degraded forensic sample.
Using this as a test bed, the authors developed a protocol that is successful in increasing/restoring missing or substandard signals at two STR loci. The protocol utilizes the bacterial RecA protein, single-stranded DNA binding protein (SSB), and bacterial DNA polymerase I, in concert with a targeting oligonucleotide.
The authors were able to show that the reactions promoted by these reagents effectively restore damaged DNA flanking a particular STR locus. The findings indicate that with the developed protocol signal restoration is successful approximately 20 percent of the time.
The findings permit the development of a method capable of physically repairing double strand breaks in damaged DNA, thereby decreasing polymerase chain reaction inhibitors (PCR) inhibition and increasing the amount of reliable STR loci in the profile. Furthermore, it requires no adaptations to current DNA analysis protocols.
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