Sequential multiplex amplification: Utility in forensic casework with minimal amounts of DNA and partially degraded samples

Since its introduction, PCR has become a widely-used, routine technique in forensic laboratories. A number of PCR protocols that were developed originally are now being replaced by more powerful approaches, particularly those based on multiplex amplification of short tandem repeat (STR) loci. One alternative form of multiplex PCR amplification, called Sequential Multiplex Amplification (SMA), was designed to amplify a single locus and then recover and reuse the remaining genomic DNA as a template for subsequent PCR. The SMA process could be repeated several times. SMA has proven to be useful in typing genomic DNA contained in stored PCR samples and analyzing samples of limited quality and/or quantity for multiple loci. The efficacy of the use of SMA for actual typing of casework samples permitted typing for a second locus 98.11% of the samples considered; 70.75% were typeable for a third locus, and 16.98% for a fourth locus.