This article reports on a collaborative study by nine European and U.S. laboratories organized under the auspices of the European DNA Profiling Group (EDNAP) for the purpose of comparing some different DNA profiling techniques for their usefulness in genotyping artificially degraded samples.
The study focused on assessing the effectiveness of new techniques, especially SNPs and mini-STRs. The study simulated a time-course series of degraded stains in their "natural state." This was achieved by incubating material spotted with saliva and blood in 100-percent humidity at 37 degrees C. . Total degradation was achieved within a short time period of 12-16 weeks. By taking samples at regular intervals, a complete time course was produced, reaching a point that corresponded to the time when little or no amplifiable DNA remained. The mini-STR assays tested yielded the best results overall when compared with standard SGM+ profiling and the Foren-SNPsTM kit. Low copy number DNA profiling proved to be the most successful method of amplification, although this technique was used by only three of the laboratories, one using Powerplex 16 and two using SGM+. Low-copy- number (LCN) profiling differs from standard DNA profiling only by the number of cycles used for PCR amplification. By increasing the number from 28 cycles to 34 cycles, the chance of amplifying the few molecules present in the DNA extract is improved; however, when LCN conditions are used, the allelic balance concurrently deteriorates, and the chance of allele dropout increases, compromising interpretation. EDNAP and the European Network of Forensic Science Institutes (ENFSI) have recommended that new multiplexes be made more efficient in detecting degraded DNA by re-engineering the STR amplicons so that primers lie closer to the repeat region. To achieve the best sensitivity, amplicons should be lower than 150 bp. 3 tables, 8 figures, and 46 references