Increasing amplification success of forensic DNA samples using multiple displacement amplification

Multiple displacement amplification (MDA) is capable of amplifying nanogram template amounts of DNA with high accuracy to generate micrograms of representative product. Although MDA is able to amplify small template amounts (<100pg), increased levels of preferential amplification and allelic dropout are observed. The use of molecular crowders (polyethylene glycol 400) can decrease the amplification bias and increase amplification success. We describe the use of standard and crowded MDA on low-concentration casework samples originating from blood, semen, saliva, hair, and trace DNA. While standard MDA produced no significant increases in STR genotyping success, the use of crowded MDA yielded an average increase of 15% in the number of alleles, with a significant decrease in the amplification bias, resulting in clearer, more-complete profiles from forensically relevant samples.