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 HLAD QA1, PM and DIS80 loci, However, preliminary validation of several STR systems for casework has demonstrated that the Chelex procedure is no t the best method of DNA isolation for STR amplifications for our purp oses. Long term storage at -20 degrees C in the presence of unbuffered Chelex beads (approximately 1 year), combined with multiple freeze th aws, resulted in signal loss at a locus for many database samples. The refore, we have employed the QIAamp spin column as an alternative meth od of DNA isolation for amplification and typing of STR loci currently being validated for use in the laboratory. Moreover, we determined th at QIAamp isolated DNA is also suitable for HLADQA1, PM and D1S80 typi ng. A matrix study was performed to determine if the QIAamp DNA proced ure would give better results on bloodstains deposited on ''problern s urfaces'' such as leather, dirt and various dyed fabrics. Again, QIAam p 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 eviden ce. with the QIAamp spin columns. The QIAamp extracted DNA performed a s well in all PCR amplification and typing procedures tested (PM, HLAD QA1, D1S80, and STR (PowerPlex)) as the phenol/chloroform Centricon is olated or EtOH precipitated DNAs. Thus we concluded that QIAamp spin c olumns are a superior method fur isolating DNA to be typed for a varie ty of loci.