Intra-bone nuclear DNA variability and STR typing success in Second World War 12th thoracic vertebrae

Bones are an important source of DNA for identification in forensic medicine, especially when the remains are skeletonized, which is the case when dealing with victims of the Second World War. Often the amount of bone available for sampling is limited, and therefore it is crucial to sample the bone segment with the highest adequate DNA quantity for identification. Studies performed on all representative skeletal element types of the human body showed that the amount of DNA obtained from different skeletal elements of different body regions varies greatly. When bones from torso were analyzed, thoracic vertebrae outperformed other vertebrae (cervical and lumbar) and, alongside the first ribs, were among the most appropriate bone elements for identification purposes. It was also shown that the quantity of DNA varies significantly within a single bone type. This study focused on exploring intra-bone DNA variability between five parts of 12th thoracic vertebrae (laminae + spinous process, pedicles + transverse processes, and corpus right, left, and middle). The research was based on the theory that the distribution of body weight and consequently bone remodeling, as well as the ratio between cancellous and cortical bone, contribute to different quantities of DNA in different parts of vertebra sampled. The vertebrae were cleaned and cut into five parts, and each part was completely ground to obtain homogenous bone powder. Half a gram of powder from each part was decalcified using a full demineralization extraction method. The DNA was purified in a Biorobot EZ1 machine (Qiagen). DNA quantity and quality were determined using the PowerQuant System (Promega) and autosomal STR typing success using the GlobalFiler Amplification Kit (Applied Biosystems). Thirty-five 12th thoracic vertebrae were sampled from a single Second World War mass grave. The best results with the highest DNA quantity were found in laminae and the spinous process, and among them all vertebrae analyzed yielded full STR profiles except three, where only a few dropouts occurred. The second-ranked bone part was the pedicles and transverse processes. The comparison of DNA degradation in the vertebral segments analyzed does not show statistically significant differences. Considering our research, when only the torso is available for identification, the 12th thoracic vertebra should be collected and the vertebral arch should be sampled for genetic analyses.