A comparison of AmpFlSTR Identifiler™ Kit versus AmpFlSTR Identifiler Plus™ Kit in challenging bone samples by using normal and increased PCR cycle number

Abstract

With the aim to increase the chance of obtaining DNA profiles from challenging forensic samples, several strategies are tested. One of the most powerful tools used in forensic DNA typing are commercial amplification kits. Enhanced buffers are provided with these kits allowing amplification of highly degraded or inhibited samples. For low DNA samples, sensitivity can be increased by raising the PCR cycle number. This study presents the results of the comparison made between Identifiler™ versus Identifiler Plus™ by using normal and increased PCR cycle number. Fifteen samples of 30–40 years post-mortem belonging to missing persons during military governments in Argentina were tested with Identifiler™ using 28 and 34 PCR cycles and with Identifiler Plus™ using 29 and 32 PCR cycles in order to compare both amplification kits. A high percentage of samples showed higher number of amplified loci with Identifiler Plus™ than with Identifiler™. This effect is more evident when increased PCR cycle number was used. Also, there were samples that exhibited identical number of amplified loci by using both kits. These samples showed high degraded DNA characteristics and the amplified loci were not the same for each amplification kit. For a group of samples that displayed flat profiles using normal PCR cycles for both kits, increased PCR cycles allowed a profile improvement that was higher using Identifiler™ with 34 PCR cycles than using Identifiler Plus™ with 32 cycles. Characteristics of highly degraded DNA or low DNA concentration were found in these samples. Furthermore, Identifiler Plus™ showed a lower percentage of locus drop-out than Identifiler™ for most of the analyzed loci and also an improved amplification success of the larger loci. On the basis of our results, Identifiler Plus™ offers a more increasing chance of DNA typing than Identifiler™ does, based on the new buffer which mainly allows overcoming PCR inhibition.