Development and Validation of MPS-Based System for Human Appearance Prediction in Challenging Forensic Samples.

Forensic DNA phenotyping (FDP) provides the ability to predict the human external traits from unknown sample donors, directly from minute amounts of DNA found at the crime scene. We developed a MPS multiplex assay, with the aim of genotyping all 41 DNA markers included in the HIrisPlex-S system for simultaneous prediction of eye, hair and skin colours. Forensic samples such as blood, skeletal remains, touch DNA, saliva swab, artificially degraded samples together with individuals with known phenotypes and a set of 2800 M control DNA were sequenced on the Ion Torrent platform in order to evaluate the concordance testing results and the forensic suitability of the 41-plex MPS assay. The panel was evaluated by testing a different number of PCR cycles and the volume of reagents for library preparation. The study demonstrated that full and reliable profiles were obtained with 0.1-5 ng, even with high degraded DNA. The increment of the number of PCR cycles results in an improvement of correctly genotyping and phenotyping for samples with low amounts of degraded DNA but higher frequencies of artefacts were found. The high DNA degradation level did not influence the correct genotyping and phenotyping and the critical parameter affecting the result is the quantity of input DNA. Eye and hair colour was predicted in 92.60% of individuals and skin colour in 85.15% of individuals. The results suggest that this MPS assay is robust, highly sensitive and useful for human pigmentation prediction in the forensic genetic field.

Assessment of the Precision ID Identity Panel kit on challenging forensic samples.

The performance of the Precision ID Identity Panel (Thermo Fisher Scientific) was assessed on a set of 87 forensic samples with different levels of degradation for which a reference sample from the "same donor" or from a "first degree relative" was available. PCR-MPS analysis was performed with DNA input ranging from 1 ng to 12 pg and through 21-26 PCR cycles, in replicate tests, and a total number of 255 libraries were sequenced on the Ion Personal Genome Machine™ (PGM™) System. The evaluation of the molecular data allowed to set a fix threshold for locus call at 50 x which suitably worked even when low amounts of degraded DNA (12 pg) were investigated. In these analytical conditions, in fact, 25 PCR cycles allowed the genotyping of about 50 % and 35 % of the autosomal and the Y-specific markers on average, respectively, for each single amplification with a negligible frequency of drop ins (0.01 %). On the other hand, drop out artefacts reached 18-23 % when low copy number and degraded DNA samples were studied, with surviving alleles showing more than 600 reads in 2.9 % of the cases. Our data pointed out that the Precision ID Identity Panel allowed accurate typing of almost any amount of good quality/moderately degraded DNA samples, in duplicate tests. The analysis of low copy number DNAs evidenced that the same allele of a heterozygous genotype could be lost twice, thus suggesting that a third amplification could be useful for a correct genotype assignment in these peculiar cases. Using the consensus approach, a limited number of genotyping errors were computed and about 37 % of the autosomal markers was finally typed with a corresponding combined random match probability of at least 1.6 × 10-13, which can be considered an excellent result for this kind of challenging samples. In the end, the results presented in this study emphasize the crucial role of the expert opinion in the correct evaluation of artefacts arising from PCR-MPS technology that could potentially lead to genetic mistyping.

Searching the undetected mtDNA variants in forensic MPS data.

The efficiency of MPS in forensic mtDNA analysis has been thoroughly proven, although a reliable and well established data evaluation still remains a critical point. Numerous bioinformatics tools have been developed, but most of them require specific operating systems and high costs, while free open-source programs with user-friendly interfaces are few. In this study, 43 full mtGenomes were sequenced using the Ion Personal Genome Machine™ (PGM™) System and analyzed utilizing the plug-in Variant Caller (TVC) of the Ion Torrent Software Suite and the mtDNA-Server (mDS), a free web-based mitochondrial analysis tool for MPS data. The outcomes of these two different analysis tools were compared to variants noted after manual inspection of the aligned reads performed using Integrative Genomics Viewer (IGV). The comparison highlighted the presence of thirty-nine discordant variant calls, which were resolved by Sanger sequencing that confirmed the presence of all variants, except for 7 deletions. The combined adoption of IGV and Sanger type sequencing confirmatory steps, in addition of TVC and mDS analysis, resulted in a more accurate variants assignment with the detection of 32 additional true polymorphisms, which were noted in the final dataset. Regarding the heteroplasmy issue, out of a total of thirty heteroplasmic variants, twenty-eight were detected by the TVC, while the mDS detected twenty-two. Overall, none of the used bioinformatics tools were the perfect choice and a secondary analysis with an expert's opinion in complete mtGenome MPS data evaluation is still required in forensic genetic analysis.

Evaluation of the Ion AmpliSeq SARS-CoV-2 Research Panel by Massive Parallel Sequencing.

Deep knowledge of the genetic features of SARS-CoV-2 is essential to track the ongoing pandemic through different geographical areas and to design and develop early diagnostic procedures, therapeutic strategies, public health interventions, and vaccines. We describe protocols and first results of the Ion AmpliSeq™ SARS-CoV-2 Research Panel by a massively parallel sequencing (MPS) assay. The panel allows for targeted sequencing by overlapping amplicons, thereby providing specific, accurate, and high throughput analysis. A modified reverse transcription reaction, which consists of the use of a SARS-CoV-2 specific primers pool from the Ion AmpliSeq SARS-CoV-2 Research Panel, was assessed in order to promote viral RNA specific reverse transcription. The aim of this study was to evaluate the effectiveness of the Ion AmpliSeq™ SARS-CoV-2 Research Panel in sequencing the entire viral genome in different samples. SARS-CoV-2 sequence data were obtained from ten viral isolates and one nasopharyngeal swab from different patients. The ten isolate samples amplified with 12 PCR cycles displayed high mean depth values compared to those of the two isolates amplified with 20 PCR cycles. High mean depth values were also obtained for the nasopharyngeal swab processed by use of a target-specific reverse transcription. The relative depth of coverage (rDoC) analysis showed that when 12 PCR cycles were used, all target regions were amplified with high sequencing coverage, while in libraries amplified at 20 cycles, a poor uniformity of amplification, with absent or low coverage of many target regions, was observed. Our results show that the Ion AmpliSeq SARS-CoV-2 Research Panel can achieve rapid and high throughput SARS-CoV-2 whole genome sequencing from 10 ng of DNA-free viral RNA from isolates and from 1 ng of DNA-free viral RNA from a nasopharyngeal swab using 12 PCR cycles for library amplification. The modified RT-PCR protocol yielded superior results on the nasopharyngeal swab compared to the reverse transcription reaction set up according to the manufacturer's instructions.

Evaluation of a microhaplotypes panel for forensic genetics using massive parallel sequencing technology.

Massive parallel DNA sequencing (MPS) makes it possible to explore a new type of genetic marker, known as microhaplotypes or microhaps. These loci were recently introduced in the landscape of forensic genetic and appear to be useful for identification purposes, reconstruction of family relationships, ancestry prediction and DNA mixtures deconvolution. Microhaplotypes loci, based on 89 loci in ALFRED, were selected and their genetic variations in 100 Italian individuals were evaluated by using MPS, in order to make inference about utility of a set of microhaps in forensic genetics. After MPS, the panel was reduced to 87 microhaps, comprised of 266 different SNPs and spread across 22 human autosomes. Genotype and haplotype frequencies were estimated, as well as the effective number of alleles at each locus (Ae), which relates to the usefulness of the locus in resolution of relationships and deconvolution of DNA mixtures. Overall, the Ae values for the 87 microhaps range from 1.010 to 8.344, with about 80% showing values greater than 2.0. Noteworthy, 32 microhaps display Ae values greater than 3.0 and 18 loci Ae above 4.0. To explore the suitability of microhaplotypes in mixture deconvolution, the probability of detecting a mixture, as a function of Ae, was inferred for different groups of loci. Considering the fourteen loci with Ae between 3.0 and 3.999 the probability of detecting a mixture was at least 0.99973, while considering the ten loci with Ae between 4.0 and 4.999 the probability was at least 0.99998. Moreover, when considering just the six loci with Ae between 5.0 and 5.999 the probability of detecting a mixture was at least 0.99984, while when considering just the two loci with Ae above 6 the probability was 0.97228. Combining these 32 MH loci, the theoretical probability of detecting a mixture was 0.999999999999973. These results make the subset of 32 loci with Ae above three informative for mixture resolution. The individual matching probabilities (PI) of the 87 microhaps ranged from 0.032 to 0.9802. Considering the 32 microhap loci with Ae greater than 3.0, the cumulative PI value was 1.6 × 10-33, while considering the 18 microhap loci with Ae above 4.0, the cumulative PI value was 2.34 × 10-21. Overall the results of this study confirmed the utility of microhaps in forensic genetics.