Characterization and performance of new MiniSTR loci for typing degraded samples

Abstract

Forensic DNA analysts often perform short tandem repeat (STR) typing on highly degraded biological material and then turn to mitochondrial DNA testing if many or all of the STRs fail. The commercially available kits for multiplex amplification of the 13 CODIS (FBI's COmbined DNA Index System) STR loci usually exhibit allele or locus-dropout for larger sized loci with degraded DNA or samples containing PCR inhibitors. By moving PCR primers closer to the STR repeat region, we have demonstrated that it is possible to obtain fully concordant results to the commercial kits while improving successful analysis of degraded DNA with smaller PCR products or “miniSTRs.” However, many of the CODIS core loci have large allele ranges (e.g., D21S11 and FGA) that make it impossible to create small PCR products. We have examined a battery of new candidate STR loci that can be made less than 100 bp in size (in many cases), and would therefore be helpful in testing highly degraded DNA samples. A set of six non-CODIS markers has been characterized and published, and the performance of these markers on degraded materials such as aged bloodstains and shed hairs has been examined. Here we report on the status of 10 additional miniSTR markers unlinked from the CODIS STR markers.