Interpretation of low-copy-number DNA profile after post-PCR purification

DNA analysis using STR amplification become increasingly sensitive permitting the use of minutes quantities of DNA transferred through skin contact. However, in such case, the interpretation of mixed profiles is very difficult due to low intensity peak, allelic drop-out or stutter increase. We use a multiple PCR strategy with post-PCR purification to help interpret low-copy-number DNA profile. To ensure that this approach can be used with minimal risk, we tested post-PCR purification of limited amount of mixed known samples. Results were analysed for correct alleles, allelic drop-out, allelic drop-in and stutter increase. No allelic drop-in was observed and most of the lowest peaks were confirmed by post-PCR purification. However, careful interpretation of peaks present at a stutter position is necessary.