QIAamp spin columns as a method of DNA isolation for forensic casework

The Detroit Police Crime Lab has historically used Chelex as a method to isolate DNA for amplification and typing of bloodstains at the HLADQA1, PM and D1S80 loci. However, preliminary validation of several STR systems for casework has demonstrated that the Chelex procedure is not the best method of DNA isolation for STR amplifications for our purposes. Long term storage at -20 degrees C in the presence of unbuffered Chelex beads (approximately 1 year), combined with multiple freeze thaws, resulted in signal loss at a locus for many database samples. Therefore, we have employed the QIAamp spin column as an alternative method of DNA isolation for amplification and typing of STR loci currently being validated for use in the laboratory. Moreover, we determined that QIAamp isolated DNA is also suitable for HLADQA1, PM and D1S80 typing. A matrix study was performed to determine if the QIAamp DNA procedure would give better results on bloodstains deposited on "problem surfaces" such as leather, dirt and various dyed fabrics. Again, QIAamp isolated DNA was more readily typeable than Chelex isolated DNA. We successfully replaced the phenol/chloroform extraction steps utilized in our laboratory for differential extractions, a commonly used method for separating sperm and non-sperm fractions of sexual assault evidence, with the QIAamp spin columns. The QIAamp extracted DNA performed as well in all PCR amplification and typing procedures tested (PM, HLADQA1, D1S80, and STR (PowerPlex)) as the phenol/chloroform Centricon isolated or EtOH precipitated DNAs. Thus we concluded that QIAamp spin columns are a superior method for isolating DNA to be typed for a variety of loci.