In forensics, hair left on a crime scene may provide important evidence in criminal investigations. At many laboratories, naturally shed hair (telogen) has not been considered suitable for STR profiling. This due to the fact that these challenging samples are expected to contain only minute amounts of highly fragmented nuclear DNA. Instead, mtDNA profiling has been the method of choice. In recent years, SNP profiling has emerged as a useful option for heavily degraded samples. However, STR profiling has been refined and current kits allows for DNA samples of lower quality and quantity to be successfully analysed. If possible to apply to hair samples, STR analysis has many benefits such as lower cost, shorter analysis time and gives the possibility to search for matches in national and international DNA databases.

We have evaluated different extraction protocols for hairs and studied the DNA extracts' potential for STR profiling. First, using hair from one donor (cut hair shafts) three different extraction protocols were evaluated: EZ1&2 DNA Investigator Kit (modified), a Chelex based method and Loreille et al. 2022 (modified). Samples were subjected to DNA quantification and STR profiling. Second, the most promising extraction protocol was applied to hairs from a number of donors to explore the variation of DNA recovered. Third, intra-individual variation in DNA yield and quality was studied using multiple hairs from a subset of the donors. Fourth, the utility of combining several STR kits was evaluated.

In summary, this study explores the success of STR profiling of human hairs following the use of three different DNA extraction protocols.

Authors

• Siri Aili Fagerholm (National Forensic Centre, Swedish Police Authority, Sweden)
• Arvid Lagerberg (National Forensic Centre, Swedish Police Authority, Sweden)
• Elin Lundkvist (National Forensic Centre, Swedish Police Authority, Sweden)
• Ricky Ansell (National Forensic Centre, Swedish Police Authority, Sweden)
• Arvid Hedén Gynnå (National Forensic Centre, Swedish Police Authority, Sweden)
• Christina Forsberg (National Forensic Centre, Swedish Police Authority, Sweden)