How to store the bone powder left after extraction for future analysis

Proper storage conditions are important for preservation of DNA. Bones are usually stored long term at −20 °C. When isolating DNA from bones, the bone powder obtained is not fully consumed. The value of retaining bone powder left after extracting DNA for future DNA analysis has been confirmed after storing bone powder for 10 years at −20 °C. Because long-term storage in a freezer is expensive and requires significant space, we were interested in whether bone powder could also be stored at room temperature without affecting the preservation of DNA. To explore this, 21 Second World War bones that generated full short tandem repeat (STR) profiles were selected, and their bone powder was stored in a freezer and at room temperature for up to 3 years. After each year, the DNA was extracted and analyzed from the stored bone powder samples. DNA was extracted using the full demineralization method employing a commercial forensic EZ1 & EZ2 DNA Investigator extraction kit (Qiagen), and automated DNA purification was performed in an EZ1 Advanced XL machine (Qiagen). Real-time PCR quantification was employed to determine the quantity and quality of DNA. The effect of different storage conditions on preservation of DNA was evaluated by determining the amount of DNA, its degradation rate, and after 3 years of storage also the success of STR genotyping. The results obtained showed no difference in the amount of DNA and degradation rate between samples stored in a freezer and at room temperature. In addition, highly informative STR profiles were obtained from all samples after 3 years of storage, regardless of whether they were stored at room temperature or were frozen. The results show no need for freezing bone powder for long-term storage, which makes it possible to save space in freezers and reduce costs.