Population studies on Caucasians from northwest Germany were carried out using the short tandem repeat (STR) systems SE 33 (Locus: ACTBP2) and TC 11 (Locus: 11p15.5). After electrophoresis in PAG 26 alleles could be identified for SE 33 in a sample size of 180 unrelated individuals and 6 alleles were found for TC 11 in 110 individuals. The combined mean exclusion chance for both systems was 0.96 and the discrimination index 0.999. No significant deviations from Hardy-Weinberg equilibrium could be demonstrated. In a small sample of families (SE 33 - n = 21; TC 11 - n = 30) no new mutations could be found. Positive and reproducible results for both STRs could be obtained from 50 pg template DNA.

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PCR primers closely flanking the repeat region were redesigned to reduce the amplicon length of the selected STRs down to approximately 100 bp for the shorter alleles (loci HumTH01, D10S2325, DYS19 and DYS391). Highly degraded DNA (e.g. formalin-fixed tissue) and very low amounts of DNA could be more successfully typed using the new redesigned primers compared to the established sequences generating longer amplicons.

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In 3 series paired volunteers were asked to gently scratch each other with the fingernails to produce superficial abrasions only of the stratum corneum. In a 4th series scratch marks were produced in the skin of cadavers but additionally including the deeper epidermal layers. Debris was removed using a thorough technique in series 1 and 2 and a careful technique in series 3. After DNA extraction, the debris was typed using the STR systems HUMACTBP2 (SE33), HUMTH01 (TC11) and HUMVWFA31 (VWA). In the material obtained from series 1 (i.e. scratching with no prior cleaning of the nails) and series 2 (i.e. cleaning of the nails prior to the experiment) the debris was removed with a sharp instrument and only the DNA pattern of the person who carried out the scratching could be detected. In the 3rd series extraneous material was removed very carefully from under the fingernails to avoid contamination with DNA from the nails. In 71% of these cases DNA patterns of the person who had been scratched or mixed DNA patterns of both persons could be detected. In the experiments with postmortem skin the DNA pattern of the cadaver could be detected in all cases. These results show that in crime cases where the perpetrator has been scratched by the victim, sufficient material can be obtained from under the fingernails for DNA typing if removal of the particles is carried out with sufficient care.