Comparison of three DNA extraction methods on bone and blood stains up to 43 years old and amplification of three different gene sequences

Extraction of amplifiable DNA-from degraded human material in the forensic context remains a problem, and maximization of yield and elimination of inhibitors of the Polymerase Chain Reaction (PCR) are important issues which rarely feature in comparative studies. The present work used PCR amplification of three DNA sequences (HLA DPB1, amelogenin and mitochondrial) to assess the efficiency of three methods for extracting DNA (sodium acetate, magnetic beads and glass-milk) from 32 skeletal samples and 25 blood stains up to 43 years old. The results, analyzed using multivariate statistics, confirmed that the extraction method was crucial to the subsequent detection of amplification products; the glass-milk protocol performed better than sodium acetate, which was better than magnetic beads. Successful amplification also depended on gene sequence, multiple copy mitochondrial sequences performing best; however, with the singly copy sequences, the longer HLA DPB1 (327 bp) being detected just as often as the shorter amelogenin (106/112 bp). Amplification products were obtained more frequently from blood stains than bone, perhaps reflecting differences inherent in the material, and from younger compared with older specimens, though plateauing seemed to occur after 10 years. PCR inhibitors were more frequent in sodium acetate extracts.