Short Tandem Repeat (STR) Profiling of Earwax DNA Obtained from Healthy Volunteers.

The present study aimed to establish human earwax as a potential source of DNA evidence that could be effectively used in human identification. Sixty earwax samples were obtained from 15 healthy male and female Saudi volunteers living in Riyadh, Saudi Arabia. Four consecutive earwax swab samples were obtained from each volunteer and stored for 1, 15, 30 and 60 days. Earwax samples were stored at room temperature (20-22 °C). Reference oral swab was also taken from each volunteer. DNA was extracted by QIAamp DNA Mini kit and quantified by real-time polymerase chain reaction (RT-PCR) on 7500 Thermal Cycler. Autosomal STR loci were amplified using AmpFLSTR™ Identifiler™ Plus PCR Amplification Kit (Thermo Fisher Scientific, Carlsbad, CA, USA). Amplified fragments were size separated and analyzed on a 3500 Genetic Analyzer. Complete autosomal STR profiles were obtained from the earwax swabs of all the volunteers stored up to 30 days after the collection. Some STR profiles were partially obtained 60 days after the earwax collection. Allelic drop-out, allelic drop-in, and stutters were seen in earwax samples analyzed 60 days after the collection. The results have shown that human earwax can be a potential source of DNA evidence for human identification up to 30 days after the earwax collection. It is recommended to quickly analyze earwax samples or store them at room temperature or at -10 °C after their recovery from the crime scene.

Population genetic data for 12 X-STR loci in the Central Saudi region using investigator Argus X-12 amplification kit.

BACKGROUND: X-chromosome short tandem repeat (X-STR) markers are important in forensic identity investigations and kinship analysis. SUBJECT AND METHODS: In the current study, the distribution of 12 X-STR loci located in four linkage groups was evaluated using Investigator® Argus X-12 Amplification Kit in 200 unrelated healthy individuals (105 males and 95 females) from the central region of Saudi Arabia in order to develop an allelic frequency database for the markers included in the kit. RESULTS: DXS10146 locus was the most informative with 21 alleles, while DXS8378 locus was the least with five alleles. Forensic parameters showed that all X-STRs loci, either as individual markers or as linkage groups, provide genetic information with high discrimination that is appropriate for forensic purposes with polymorphism information content (PIC), power of exclusion (PE), and paternity index (PI) varying from 0.61211 to 0.917979, 0.38722 to 0.842949, and 0.038416 to 0.16367, respectively. The pairwise genetic distance fixation index (Fst) results showed that the Saudi population is genetically closer to the Egyptian and Emirati populations and distant to the Turkish population. CONCLUSION: The current study revealed that Investigator® Argus 12 X-STR kit would support the forensic application, kinship testing involving female offspring, and human identification in the Saudi population.

The impact of chimerism on DNA-based human identification from skin surface cells of post-allogenic hematopoietic stem cell transplantation (HCST) patients.

The use of biological traces recovered from touched or handled items increased with the advance of the forensic analysis system. Thus, DNA profiles obtained from touch DNA became a useful tool in forensic investigation. However, a chimeric person with more than one chromosomal population can be challenging for a forensic analyst. We investigated the genetic profile in blood, buccal swab, and skin swabs from twenty-four recipients aged 21-63 years who underwent a matched sibling allogeneic hematopoietic stem cell transplantation with no sign of skin graft versus host disease. Autosomal short tandem repeats genotyping was performed to evaluate chimerism status at 15 loci along with gender marker Amelogenin. According to our results, donor chimerism was detected in all recipient's blood samples, while in buccal swabs, five recipients showed no presence of donor-derived cells in their genotype. Epithelial cells swabbed from hand fingertips were not devoid of donor-derived cells since all recipients showed high chimerism (39.69%-96.66%) in their genotypes. A significant change in chimerism was seen among various types of biological samples (p<0.05). No correlations were observed between chimerism and recipient age, gender, or time after transplant (p> 0.05). The loci D21S11, D8S1179, and FGA were the most informative, whereas D13S317, Vwa, and TOPX were the least informative STR markers. We concluded that touch DNA from a person who has undergone a successful allogeneic HSCTs should not be considered as reliable evidence for human identifications. Therefore, necessary precautions must be taken to avoid false identification and miscarriage of justice.

Evaluation of Skin Surface as an Alternative Source of Reference DNA Samples: A Pilot Study.

An acceptable area for collecting DNA reference sample is a part of the forensic DNA analysis development. The aim of this study was to evaluate skin surface cells (SSC) as an alternate source of reference DNA sample. From each volunteer (n = 10), six samples from skin surface areas (forearm and fingertips) and two traditional samples (blood and buccal cells) were collected. Genomic DNA was extracted and quantified then genotyped using standard techniques. The highest DNA concentration of SSC samples was collected using the tape/forearm method of collection (2.1 ng/µL). Cotton swabs moistened with ethanol yielded higher quantities of DNA than swabs moistened with salicylic acid, and it gave the highest percentage of full STR profiles (97%). This study supports the use of SSC as a noninvasive sampling technique and as a extremely useful source of DNA reference samples among certain cultures where the use of buccal swabs can be considered socially unacceptable.