Comparison of nuclear DNA yield and STR typing success in Second World War petrous bones and metacarpals III

Evaluation of a New DNA Extraction Method on Challenging Bone Samples Recovered from a WWII Mass Grave

Bones and teeth represent a common finding in ancient DNA studies and in forensic casework, even after a long burial. Genetic typing is the gold standard for the personal identification of skeletal remains, but there are two main factors involved in the successful DNA typing of such samples: (1) the set-up of an efficient DNA extraction method; (2) the identification of the most suitable skeletal element for the downstream genetic analyses. In this paper, a protocol based on the processing of 0.5 g of bone powder decalcified using Na2EDTA proved to be suitable for a semi-automated DNA extraction workflow using the Maxwell® FSC DNA IQ™ Casework Kit (Promega, Madison, WI, USA). The performance of this method in terms of DNA recovery and quality was compared with a full demineralisation extraction protocol based on Qiagen technology and kits. No statistically significant differences were scored according to the DNA recovery and DNA degradation index (p-values ≥ 0.176; r ≥ 0.907). This new DNA extraction protocol was applied to 88 bone samples (41 femurs, 19 petrous bones, 12 metacarpals and 16 molars) allegedly belonging to 27 World War II Italian soldiers found in a mass grave on the isle of Cres (Croatia). The results of the qPCR performed by the Quantifiler Human DNA Quantification kit showed values above the lowest Limit of Quantification (lLOQ; 23 pg/µL) for all petrous bones, whereas other bone types showed, in most cases, lower amounts of DNA. Replicate STR-CE analyses showed successful typing (that is, >12 markers) in all tests on the petrous bones, followed by the metacarpals (83.3%), femurs (52.2%) and teeth (20.0%). Full profiles (22/22 autosomal markers) were achieved mainly in the petrous bones (84.2%), followed by the metacarpals (41.7%). Stochastic amplification artefacts such as drop-outs or drop-ins occurred with a frequency of 1.9% in the petrous bones, whereas they were higher when the DNA recovered from other bone elements was amplified (up to 13.9% in the femurs). Overall, the results of this study confirm that petrous bone outperforms other bone elements in terms of the quantity and quality of the recovered DNA; for this reason, if available, it should always be preferred for genetic testing. In addition, our results highlight the need for accurate planning of the DVI operation, which should be carried out by a multi-disciplinary team, and the tricky issue of identifying other suitable skeletal elements for genetic testing. Overall, the results presented in this paper support the need to adopt preanalytical strategies positively related to the successful genetic testing of aged skeletal remains in order to reduce costs and the time of analysis.

An optimal skeletal element for DNA testing: Evaluation of DNA quantity and quality from various bone types in routine forensic practice

For human identification, the quality and quantity of DNA must be sufficient for amplification and analysis. When DNA extraction from bone tissues and teeth is required, the optimal skeletal elements should be selected as samples for DNA extraction because DNA yield differs among elements. Recently, some studies have reported that a high quantity of high-quality DNA can be extracted from the small cancellous bones of the hands and feet. In this study, we evaluated the effectiveness of small cancellous bones in the human identification of skeletal remains in routine forensic genetic casework. Cancellous bones [phalanges, (meta)carpal bones, and (meta)tarsal bones)] and the cortical bones (femur and petrous bones) and teeth, which have generally been recommended as samples, were collected from the same individuals that needed identifying using DNA analysis in our laboratory. The quantity of DNA from small cancellous bones tended to be higher than that from cortical bones, and the quality from the former was as high as that from the latter. This study showed that in routine forensic casework, the small cancellous bones of the hands and feet should be actively selected as samples for DNA testing.

Genetic sexing of subadult skeletal remains

When subadult skeletons need to be identified, biological sex diagnosis is one of the first steps in the identification process. Sex assessment of subadults using morphological features is unreliable, and molecular genetic methods were applied in this study. Eighty-three ancient skeletons were used as models for poorly preserved DNA. Three sex-informative markers on the Y and X chromosome were used for sex identification: a qPCR test using the PowerQuant Y target included in PowerQuant System (Promega), the amelogenin test included in ESI 17 Fast STR kit (Promega), and a Y-STR amplification test using the PowerPlex Y-23 kit (Promega). Sex was successfully determined in all but five skeletons. Successful PowerQuant Y-target, Y-amelogenin, and Y-chromosomal STR amplifications proved the presence of male DNA in 35 skeletons, and in 43 subadults female sex was established. No match was found between the genetic profiles of subadult skeletons, and the elimination database and negative control samples produced no profiles, indicating no contamination issue. Our study shows that genetic sex identification is a very successful approach for biological sexing of subadult skeletons whose sex cannot be assessed by anthropological methods. The results of this study are applicable for badly preserved subadult skeletons from routine forensic casework.

Measure quantity of mitochondrial DNA in aged bones or calculate it from nuclear DNA quantitative PCR results?

Mitochondrial DNA (mtDNA) is of great value in forensics to procure information about a person when a next of kin, personal belongings, or other sources of nuclear DNA (nDNA) are unavailable, or nDNA is lacking in quality and quantity. The quality and reliability of the results depend greatly on ensuring optimal conditions for the given method, for instance, the optimal input of the copy number (CN) in next-generation sequencing (NGS) methods. The unavailability of commercial quantitative PCR (qPCR) methods to determine mtDNA CN creates the necessity to rely on recommendations to infer mtDNA CN from nDNA yield. Because nDNA yield varies between individuals, tissues, parts of the same tissue, and because mtDNA CN varies between tissues, such assumptions must be examined for a specific context, rather than be generalized. This study compares mtDNA CN calculated from nDNA yield and qPCR measured mtDNA CN. Seventy-five femurs from the Second World War victims were used as samples; they were cut below the greater trochanter, surface contaminants were removed by mechanical and chemical cleaning, samples were fully demineralized, and DNA was isolated. PowerQuant® Kit (Promega) was used to analyze DNA yield. An in-house method was used to determine mtDNA CN. Comparison of mtDNA CN from nDNA derived calculations and measured mtDNA CN highlighted vast differences. The results emphasize the need to perform qPCR to assess mtDNA CN before NGS analyses of aged bones' mitogenomes rather than estimating mtDNA CN from nDNA yield to ensure the quality and reliability of the results of NGS analysis.

A comparison between petrous bone and tooth, femur and tibia DNA analysis from degraded skeletal remains

Skeletal remains are the only biological material that remains after long periods; however, environmental conditions such as temperature, humidity, and pH affect DNA preservation, turning skeletal remains into a challenging sample for DNA laboratories. Sample selection is a key factor, and femur and tooth have been traditionally recommended as the best substrate of genetic material. Recently, petrous bone (cochlear area) has been suggested as a better option due to its DNA yield. This research aims to evaluate the efficiency of petrous bone compared to other cranium samples (tooth) and postcranial long bones (femur and tibia). A total amount of 88 samples were selected from 38 different individuals. The samples were extracted by using an organic extraction protocol, DNA quantification by Quantifiler Trio kit and amplified with GlobalFiler kit. Results show that petrous bone outperforms other bone remains in quantification data, yielding 15-30 times more DNA than the others. DNA profile data presented likeness between petrous bone and tooth regarding detected alleles; however, the amount of DNA extracted in petrous bones allowed us to obtain more informative DNA profiles with superior quality. In conclusion, petrous bone or teeth sampling is recommended if DNA typing is going to be performed with environmentally degraded skeletal remains.

Comparison of DNA preservation between adult and non-adult ancient skeletons

Studies evaluating DNA preservation in non-adults, or comparing preservation in adults and non-adults, are very rare. This study compares the preservation of DNA in the skeletal remains of adults and non-adults. It compares the quality and quantity of DNA recovered from different skeletal elements of adults and non-adults, and from non-adults of different age classes. In addition, the preservation of DNA in males and females is compared. Bone DNA preservation was estimated by measuring nuclear DNA concentration and its degradation, and through STR typing success. The study analyzed 29 adult skeletons and 23 non-adult skeletons from the Ljubljana-Polje archeological site, dating from the seventeenth to nineteenth century, and up to four skeletal elements (petrous bone, femur, calcaneus, and talus) were included. After full demineralization extraction, the PowerQuant System and the PowerPlex ESI 17 Fast System (Promega) were used for qPCR and STR typing, respectively. The results showed that, among the four bone types analyzed, only the petrous bone proved to be a suitable source of DNA for STR typing of non-adult skeletal remains, and DNA yield is even higher than in the adult petrous bone, which can be attributed to the higher DNA degradation observed in the adult petrous bone. In adult skeletons, petrous bones and tali produced high STR amplification success and low DNA yield was observed in adult femurs. The results of this study are applicable for the sampling strategy in routine forensic genetics cases for solving identification cases, including badly preserved non-adult and also adult skeletons.