Consensus profiles and databasing of casework samples amplified with 34 PCR cycles: an empirical approach

Forensic laboratories commonly have to analyze samples that contain minute amounts of DNA (Low Copy Number DNA). LCN samples can be amplified with increased numbers of PCR cycles, but stochastic variations of their profiles are generally observed. Here, we compare some characteristics of the AmplSTR SGM Plus profiles from casework samples amplified with 28 and 34 cycles in order to evaluate the interpretation guidelines used in our laboratory to genotype LCN samples. A first striking result was that 60% of the 563 casework samples considered yielded DNA concentrations <200 pg/Al DNA and were considered as LCN. Conclusive profiles were recovered for 142 of them (42%). At the end, 142 profiles amplified with 28 cycles and 119 profiles amplified with 34 cycles were sent to the Swiss data base. Respectively, 43.66% and 43.70% of them made a hit. This suggests that reliable LCN profiles can be obtained when using an adapted strategy. D 2003 Elsevier B.V. All rights reserved.