Efficient DNA extraction from hair shafts

Abstract

Hairs are common biological samples in crime scene investigation. However, most of this evidence is comprised of hair fragments without the root. As the major part of DNA is located in the root, hair shafts are usually problematic samples in forensic analysis. For these reasons, hair DNA typing is directed at mitochondrial DNA (mtDNA), which is present in high copy number in each cell, instead of nuclear DNA analysis. In our laboratory, we have used the PrepFiler BTA (TM) extraction method for routinely processing difficult samples such as old bones or cigarette butts, obtaining good quality DNA in all cases. As the use of automatic extraction methods has been progressively introduced in forensic laboratories, we have tested the applicability of the PrepFiler BTA (TM) extraction method in combination with AutoMate Express (TM) equipment, to the analysis of hair shafts. In order to determine the efficiency of the method, DNA extractions were quantified using a real-time PCR approach, and mtDNA fragments of different lengths were amplified to determine DNA degradation. We also processed several types of hairs, with different characteristics (thickness, gender, antiquity and hair dyeing) and from diverse ethnical groups. In all cases, the PrepFiler BTA Express (TM) extraction method showed very reproducible results in obtaining DNA from hair shafts, its application being highly recommendable as a routine protocol in forensic laboratories.