The impact of DNA contamination of bone samples in forensic case analysis and anthropological research.

Contamination precautions and quality control are great issues when human bones are investigated genetically. This is especially true for historical samples with only minute amounts of usually highly degraded DNA. But also in forensic routine analysis, sometimes DNA has to be isolated from bones in equally bad conditions, e.g. from burned victims. In such cases, there are several eventualities to contaminate the sample with foreign DNA, for example caused by the recovery of the bones, by trace investigation on a crime scene, or - of course - during handling in the lab. We present the investigation of artificially contaminated historical bone samples which contained no original DNA. Three different kind of contamination were studied: (1) touching of the samples, (2) application of saliva, and (3) application of pure DNA. The samples were genetically investigated without and with the employment of a defined cleaning protocol of the bones. The results show that pure DNA can usually not be removed from the bones and that saliva is a similar thread for subsequent DNA analysis. After the cleaning procedure about 70% of saliva contaminated samples still yielded reproducible STR profiles implicating severe problems for the investigation of highly degraded bone fragments. Simple touching of the specimens seems not to be a real problem for genetic investigations since the obtained signals were not reproducible.