A quantitative assessment of a reliable screening technique for the STR analysis of telogen hair roots

Human telogen hairs are commonly recovered as trace evidence but currently have limited use for forensic DNA analysis. Recent studies have revealed that telogen roots may be shed with adhering material that may contain cells, thus providing a potential source of nuclear DNA. A simple histological stain can be used to screen telogen roots for the presence of nuclei, thus increasing the chance of selecting roots that may yield nuclear DNA. Using this method to visualise nuclei, we surveyed 998 hairs from 136 individuals, quantified the number of nuclei, extracted DNA and evaluated corresponding DNA yield and STR profiling success. Of the hairs screened, 35% of telogen roots contained nuclei and in total 6% of all roots screened had more than 100 nuclei. The number of nuclei associated with telogen roots was independent of the presence or absence of visibly adhering material, highlighting the importance of using histological staining rather than simple microscopic examination. DNA yield and STR profiling were significantly and positively correlated with nuclei number. The methods presented here can be incorporated into routine trace and DNA analysis providing an efficient and cost effective method to screen telogen hairs, and predict STR profiling success prior to destructive DNA analysis. The results of this study indicate telogen hairs may provide a reliable source of nuclear DNA for use in routine casework.