A fluorescent microscopy-screening test for efficient STR-typing of telogen hair roots

Nuclear DNA-profiling from human hairs is a well-known technique in forensic investigations, but its success rate is quite low with some hair types. As nuclear DNA (nuDNA) extracted from telogen hair roots is in short supply and is often degraded, a simple and effective method of estimating the number of nuclear DNAs in telogen roots has been developed. DAPI, a fluorescent, non-destructive DNA stain, allows the visualization of "nuclei" (DAPI-positive spots the shape and size of the human follicular cell nuclei) and does not interfere with subsequent PCR analyses. We stained 3242 telogen roots from 27 donors. Surprisingly, of the 2572 club roots without any soft tissue remnants 11% contained visible "nuclei" and 3.3% even contained many. At the same time 57% of the 670 telogen roots with soft tissue remnants did not show any fluorescent "nuclei". We analysed the STR-profile of some of the roots selected by the DAPI screening, i.e. 132 telogen roots without soft tissue remnants, with a success rate of 79%. Our proposed screening method allows the DNA laboratory to analyse nuclear DNA only in the most promising hair roots.