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The top challenges of adopting new methods to forensic DNA analysis in routine laboratories are often the capital investment and the expertise required to implement and validate such methods locally. In the case of next-generation sequencing, in the last decade, several specifically forensic commercial options became available, offering reliable and validated solutions. Despite this, the readily available expertise to analyze, interpret and understand such data is still perceived to be lagging behind. This review gives an introductory overview for the forensic scientists who are at the beginning of their journey with implementing next-generation sequencing locally and because most in the field do not have a bioinformatics background may find it difficult to navigate the new terms and analysis options available. The currently available open-source and commercial software for forensic sequencing data analysis are summarized here to provide an accessible starting point for those fairly new to the forensic application of massively parallel sequencing.

In recent years a number of computer-based algorithms have been developed for the deconvolution of complex DNA mixtures in forensic science. These procedures utilize likelihood ratios that quantify the evidence for a hypothesis for the presence of a person of interest in a DNA profile compared to an alternative hypothesis. Proper operation of these software systems requires an assumption regarding the total number of contributors present in the mixture. Unfortunately, estimates based on counting the number of alleles at a locus can be inaccurate due to the sharing and masking of alleles at individual loci. The effects of allele masking become increasingly severe as the number of contributors increases, rendering estimates about high-order mixtures uncertain. The accuracy of these estimates can be improved by increasing the number of STR markers in panels, and by using highly polymorphic markers. Increasing the number of STR markers from 13 to 20 (expanded CODIS panel) improves the accuracy of allele count-based estimation methods for low-order mixtures, but accuracy for high-order mixtures (> 3 contributors) remains poor due to allele masking. An alternative technique, massively parallel sequencing, holds great potential to improve the accuracy of the estimate of number of contributors due to its ability to detect sequence polymorphisms within alleles. This process results in an expansion of the number of alleles when compared to that obtained using capillary electrophoresis. Here, we show that the detection of these additional sequence-defined alleles in 22-marker panels improves number of contributor estimates in conceptual mixtures of 4 and 5 contributors.

The application of massively parallel sequencing (MPS) to forensic genetics has led to improvements in multiple aspects of DNA analysis, however, additional complexities are concurrently associated with these advances. In relation to short tandem repeat (STR) typing, the move to sequence rather than length-based methodologies has highlighted the extent to which previous allelic variation was masked – both within and outside of the repeat regions (the flanking regions). In order to fully implement MPS for autosomal STR analysis, sequence-based allelic frequencies must be available, and concordance with previous typing techniques needs to be assessed. In this work, a series of samples (n = 1007) from five different population groups were genotyped using the MiSeq FGx™ Forensic Genomics System. Results were compared to those obtained using capillary electrophoresis (CE), and sequence variation has been characterised both within and outside STR repeat regions, with allelic frequencies provided for all variants observed within this database. Analysing and characterising flanking region sequence is currently less straightforward than studying repeat region variation alone, and the added value of doing so remains largely unexplored – this paper provides data to show that the gain in polymorphism achieved when analysing flanking regions is less than might be expected. In the White British population for example, including the sequence variation within repeat regions of 26 autosomal STRs made the average combined random match probability (RMP) over 700 times lower than with length-based alleles alone. Including the sequence variation within the flanking regions only resulted in a combined RMP that was a further 4 times lower.

This manuscript reports Short Tandem Repeat (STR) sequence-based allele frequencies for 1036 samples across 27 autosomal STR loci: D1S1656, TPOX, D2S441, D2S1338, D3S1358, D4S2408, FGA, D5S818, CSF1PO, D6S1043, D7S820, D8S1179, D9S1122, D10S1248, TH01, vWA, D12S391, D13S317, Penta E, D16S539, D17S1301, D18S51, D19S433, D20S482, D21S11, Penta D, and D22S1045. Sequence data were analyzed by two bioinformatic pipelines and all samples have been evaluated for concordance with alleles derived from CE-based analysis at all loci. Each reported sequence includes high-quality flanking sequence and is properly formatted according to the most recent guidance of the International Society for Forensic Genetics. In addition, GenBank accession numbers are reported for each sequence, and associated records are available in the STRSeq BioProject (https://www.ncbi.nlm.nih.gov/bioproject/380127). The D3S1358 locus demonstrates the greatest average increase in heterozygosity across populations (approximately 10 percentage points). Loci demonstrating average increase in heterozygosity from 10 to 5 percentage points include (in descending order) D9S1122, D13S317, D8S1179, D21S11, D5S818, D12S391, and D2S441. The remaining 19 loci each demonstrate less than 5 percentage point increase in average heterozygosity. Discussion includes the utility of this data in understanding traditional CE results, such as informing stutter models and understanding migration challenges, and considerations for population sampling strategies in light of the marked increase in rare alleles for several of the sequence-based STR loci. This NIST 1036 data set is expected to support the implementation of STR sequencing forensic casework by providing high-confidence sequence-based allele frequencies for the same sample set which are already the basis for population statistics in many U.S. forensic laboratories.

In a previous study we presented an assay for targeted mRNA sequencing for the identification of human body fluids, optimised for the Illumina MiSeq/FGx MPS platform. This assay, together with an additional in-house designed assay for the Ion Torrent PGM/S5 platform, formed the basis for a collaborative exercise within 17 EUROFORGEN and EDNAP laboratories, in order to test the efficacy of targeted mRNA sequencing to identify body fluids. The task was to analyse the supplied dried body fluid stains and, optionally, participants’ own bona fide or mock casework samples of human origin, according to specified protocols. The provided primer pools for the Illumina MiSeq/FGx and the Ion Torrent PGM/S5 platforms included 33 and 29 body fluid specific target sequences, respectively, to identify blood, saliva, semen, vaginal secretion, menstrual blood and skin. The results demonstrated moderate to high count values in the body fluid or tissue of interest with little to no counts in non-target body fluids. There was some inter-laboratory variability in read counts, but overall the results of the laboratories were comparable in that highly expressed markers showed high read counts and less expressed markers lower counts. We performed a partial least squares analysis (PLS) on the data, where blood, menstrual blood, saliva and semen markers and samples clustered well. The results of this collaborative mRNA massively parallel sequencing (MPS) exercise support targeted mRNA sequencing as a reliable body fluid identification method that could be added to the repertory of forensic MPS panels.

The higher level of multiplexing possible with current sequencing technologies encourages adoption of additional STR loci to aid in mixture interpretation [1] . However, characterization of these loci and orientation on the human genome is vital for interlaboratory comparability and databasing. Currently, when a laboratory publishes population data from a locus not previously characterized for forensic use, there is no robust way to verify the locus designation, repeat region format, and fidelity of target. To address this, we have evaluated short- and long-read sequence data generated for reference materials included in the Genome in a Bottle Consortium (GIAB) [2] with the goal of reporting STR sequences for loci which may be of interest to the forensic community. Initially, we have analyzed GIAB data using Marshfield sets of primers (published in [3] ), targeting over 600 microsatellite loci with STRaitRazor 3.0 [4] . In the future, this approach can be expanded to include other loci of interest. High-confidence STR sequence data will be made publicly available via GenBank record creation within the STRSeq BioProject [5] . As the cell lines represented in GIAB reference materials are available for purchase, this STR dataset represents a robust method for researchers to confirm targeted loci.

A collaborative European DNA Profiling (EDNAP) Group exercise was undertaken to assess the performance of an earlier described SNaPshot™-based screening assay (denoted mini-mtSNaPshot) (Weiler et al., 2016) [1] that targets 18 single nucleotide polymorphism (SNP) positions in the mitochondrial (mt) DNA control region and allows for discrimination of major European mtDNA haplogroups. Besides the organising laboratory, 14 forensic genetics laboratories were involved in the analysis of 13 samples, which were centrally prepared and thoroughly tested prior to shipment. The samples had a variable complexity and comprised straightforward single-source samples, samples with dropout or altered peak sizing, a point heteroplasmy and two-component mixtures resulting in one to five bi-allelic calls. The overall success rate in obtaining useful results was high (97.6%) given that some of the participating laboratories had no previous experience with the typing technology and/or mtDNA analysis. The majority of the participants proceeded to haplotype inference to assess the feasibility of assigning a haplogroup and checking phylogenetic consistency when only 18 SNPs are typed. To mimic casework procedures, the participants compared the SNP typing data of all 13 samples to a set of eight mtDNA reference profiles that were described according to standard nomenclature (Parson et al., 2014) [2], and indicated whether these references matched each sample or not. Incorrect scorings were obtained for 2% of the comparisons and derived from a subset of the participants, indicating a need for training and guidelines regarding mini-mtSNaPshot data interpretation.

In a previous EUROFORGEN/EDNAP collaborative exercise, we tested two assays for targeted mRNA massively parallel sequencing for the identification of body fluids/tissues, optimized for the Illumina MiSeq/FGx and the Ion Torrent PGM/S5 platforms, respectively. The task of the second EUROFORGEN/EDNAP collaborative exercise was to analyze dried body fluid stains with two different multiplexes, the former Illumina 33plex mRNA panel for body fluid/tissue identification and a 35plex cSNP panel for assignment of body fluids/tissues to donors that was introduced in a proof-of-concept study recently. The coding region SNPs (cSNPs) are located within the body fluid specific mRNA transcripts and represent a direct link between the body fluid and the donor. We predicted the origin of the stains using a partial least squares discriminant analysis (PLS-DA) model, where most of the single source samples were correctly predicted. The mixed body fluid stains showed poorer results, however, at least one component was predicted correctly in most stains. The cSNP data demonstrated that coding region SNPs can give valuable information on linking body fluids/tissues with donors in mixed body fluid stains. However, due to the unfavorable performance of some cSNPs, the interpretation remains challenging. As a consequence, additional markers are needed to increase the discrimination power in each body fluid/tissue category.

Sequencing short tandem repeat (STR) loci allows for determination of repeat motif variations within the STR (or entire PCR amplicon) which cannot be ascertained by size-based PCR fragment analysis. Sanger sequencing has been used in research laboratories to further characterize STR loci, but is impractical for routine forensic use due to the laborious nature of the procedure in general and additional steps required to separate heterozygous alleles. Recent advances in library preparation methods enable high-throughput next generation sequencing (NGS) and technological improvements in sequencing chemistries now offer sufficient read lengths to encompass STR alleles. Herein, we present sequencing results from 183 DNA samples, including African American, Caucasian, and Hispanic individuals, at 22 autosomal forensic STR loci using an assay designed for NGS. The resulting dataset has been used to perform population genetic analyses of allelic diversity by length compared to sequence, and exemplifies which loci are likely to achieve the greatest gains in discrimination via sequencing. Within this data set, six loci demonstrate greater than double the number of alleles obtained by sequence compared to the number of alleles obtained by length: D12S391, D2S1338, D21S11, D8S1179, vWA, and D3S1358. As expected, repeat region sequences which had not previously been reported in forensic literature were identified.

The introduction of massively parallel sequencing (MPS) to forensic genetics has led to improvements in multiple aspects of DNA analysis, however additional complexities are concurrently associated with these advances. In relation to STR analysis, the move to assign alleles using sequence rather than length based methodologies has highlighted the extent to which previous allelic variation was masked. In this work, a series of samples (n=1000) from five different population groups (Caucasian, West African, North East African, East Asian and South Asian) were genotyped for 27 forensically validated autosomal STRs. Results were compared to data from the National Institute of Standards and Technology (NIST), with this collaborative project now providing one of the most expansive data sets generated using MPS technology to date. The large number of these variants characterised at select markers brings into question the strategies for producing representative population data, yet also provides an opportunity to utilise this diversity in unique ways. Results from this collaborative study have demonstrated that the number of samples necessary to capture the breadth of allelic variation is highly dependent on the individual marker and the extent of its sequence variability.

Next Generation Sequencing (NGS) is transforming the landscape of the Short Tandem Repeat (STR) genotyping. NGS determines the length as well as the sequence of each allele, identifies polymorphisms in the repeat or adjacent DNA regions, allows for a greater degree of multiplexing, and generates Gigabases of reads in a single run. An additional step introduced into the DNA typing process with NGS methods is library preparation. The PCR amplicons of the targeted loci are further purified and modified with adapters and sample specific indices prior to sequencing. In this study, two PCR purification methods were used to cleanup amplification reactions prior to library construction: column-based and bead-based technologies. The influence of different PCR purification protocols on the dropout events was examined.

At the 27th ISFG meeting in Seoul, we presented STRSeq, a catalog of high-confidence sequences at forensic short tandem repeat (STR) loci targeted in commercially available sequencing assays. This project was initiated to facilitate the description of sequence-based alleles, providing a framework for communication among laboratories. The STRSeq catalog is maintained at NCBI, in the form of GenBank records organized in a BioProject hierarchy. Herein we describe a method by which a user can query this catalog using the NCBI BLAST application.

The National Institute of Standards and Technology (NIST) U.S. population sample set of unrelated individuals was used to determine allele and haplotype frequencies for seven X-chromosome short tandem repeat (STR) loci in four linkage groups. DXS7132, DXS7423, DXS8378, DXS10074, DXS10103, DXS10135, and HPRTB were sequenced using the ForenSeq DNA Signature Prep Kit on a MiSeq FGx instrument from Verogen. Capillary electrophoresis data produced using the Qiagen Investigator Argus X-12 was compared to ForenSeq length-based alleles and found to be 99 % concordant. For three loci (DXS10103, DXS10074, and HPRTB) the length-based allele call is affected by the extent of flanking region included in the reported sequence. Six of the seven loci gained alleles by sequencing compared to length-based determinations. The increase in alleles are found in both the repeat and flanking region sequences. All sequences for which frequencies are reported in this dataset were cataloged as GenBank records in the STRSeq NCBI BioProject ( https://www.ncbi.nlm.nih.gov/bioproject/380127 ). Frequency information for both the loci and linkage groups is reported, along with results of statistical tests including gene diversity, polymorphism information content, power of discrimination, and linkage disequilibrium. All supplemental files are available at the NIST Public Data Repository – U.S. population data for Human Identification Markers ( https://doi.org/10.18434/t4/1500024 ).

A set of 1036 U.S. Population Samples were sequenced using the Illumina ForenSeq DNA Signature Prep Kit. This sample set has been highly characterized using a variety of marker systems for human identification. The FASTQ files obtained from a ForenSeq DNA Signature Prep Kit experiment include several STR loci that are not reported in the associated software. These include SE33, DXS8377, DXS10148, DYS456, and DYS461. The sequence variation within the autosomal STR marker SE33 was evaluated using a customized bioinformatic approach to identify and characterize the locus in the 1036 data set. The analysis identified 53 unique alleles by length and 264 by sequence. An additional 10 alleles were detected when selected extended flanking regions were examined to resolve discordances. Allele frequencies and SE33 sequence motif patterns are reported for the 1036 data set. The comparison of numerical allele calls derived from sequence data to the allele calls obtained from commercial capillary electrophoresis-based STR typing kits resulted in 100% concordance, after manual data review and confirmation sequencing of three flanking region deletions. The analysis of this data set involved significant manual sequence curation and information support from length-based genotypes to ensure high confidence in the sequence-based allele calls. The challenges of interpreting the sequence data for SE33 consisted of high sequence noise, allele-size dependent variance in coverage, and heterozygote imbalance. As allele length increased, sequence depth of coverage and quality decreased at the terminal end. Accordingly, heterozygous genotype imbalance increased in proportion to increased distance between alleles.

Sequencing short tandem repeat (STR) markers on the Y chromosome allows for characterization of repeat motif variations within the Y-STR marker that cannot be determined by length-based fragment analysis with capillary electrophoresis (CE). Two commercial sequence-based assays have been run at the U.S. National Institute of Standards and Technology (NIST) with U.S. population samples (Caucasian, Hispanic, African American and Asian). The ForenSeq DNA Signature Prep Kit and prototype PowerSeq 46GY System contain a total of 27 Y-STR markers between the two kits (DYF387S1, DYS19, DYS385a/b, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438, DYS439, DYS448, DYS456, DYS458, DYS460, DYS481, DYS505, DYS522, DYS533, DYS549, DYS570, DYS576, DYS612, DYS635, DYS643, and Y-GATA-H4). Data analysis was performed using an in-house pipeline based on open source software. The resulting data reveals the degree of information gained through sequencing Y-STR markers and will be illustrated per population for the 27 markers. Allele calls from corresponding CE data were compared to sequence data for concordance. Discordant allele calls were further investigated to assess underlying causes such as null alleles, imbalanced peaks in multi-copy markers, flanking region insertions/deletions (indels), copy number variations, high stutter, and artifacts.

There is increasing interest in forensic ancestry tests, which are part of a growing number of DNA analyses that can enhance routine profiling by obtaining additional genetic information about unidentified DNA donors. Nearly all ancestry tests use single nucleotide polymorphisms (SNPs), but these currently rely on SNaPshot single base extension chemistry that can fail to detect mixed DNA. Insertion-deletion polymorphism (Indel) tests have been developed using dye-labeled primers that allow direct capillary electrophoresis detection of PCR products (PCR-to-CE). PCR-to-CE maintains the direct relationship between input DNA and signal strength as each marker is detected with a single dye, so mixed DNA is more reliably detected. We report the results of a collaborative inter-laboratory exercise of 19 participants (15 from the EDNAP European DNA Profiling group) that assessed a 34-plex SNP test using SNaPshot and a 46-plex Indel test using PCR-to-CE. Laboratories were asked to type five samples with different ancestries and detect an additional mixed DNA sample. Statistical inference of ancestry was made by participants using the Snipper online Bayes analysis portal plus an optional PCA module that analyzes the genotype data alongside calculation of Bayes likelihood ratios. Exercise results indicated consistent genotyping performance from both tests, reaching a particularly high level of reliability for the Indel test. SNP genotyping gave 93.5% concordance (compared to the organizing laboratory's data) that rose to 97.3% excluding one laboratory with a large number of miscalled genotypes. Indel genotyping gave a higher concordance rate of 99.8% and a reduced no-call rate compared to SNP analysis. All participants detected the mixture from their Indel peak height data and successfully assigned the correct ancestry to the other samples using Snipper, with the exception of one laboratory with SNP miscalls that incorrectly assigned ancestry of two samples and did not obtain informative likelihood ratios for a third. Therefore, successful ancestry assignments were achieved by participants in 92 of 95 Snipper analyses. This exercise demonstrates that ancestry inference tests based on binary marker sets can be readily adopted by laboratories that already have well-established CE regimes in place. The Indel test proved to be easy to use and allowed all exercise participants to detect the DNA mixture as well as achieving complete and concordant profiles in nearly all cases. Lastly, two participants successfully ran parallel next-generation sequencing analyses (each using different systems) and achieved high levels of genotyping concordance using the exercise PCR primer mixes unmodified. (C) 2015 Elsevier Ireland Ltd. All rights reserved.

The STR Sequencing Project (STRSeq) was initiated to facilitate the description of sequence-based alleles at the Short Tandem Repeat (STR) loci targeted in human identification assays. This international collaborative effort, which has been endorsed by the ISFG DNA Commission, provides a framework for communication among laboratories. The initial data used to populate the project are the aggregate alleles observed in targeted sequencing studies across four laboratories: National Institute of Standards and Technology (N = 1786), Kings College London (N = 1043), University of North Texas Health Sciences Center (N = 839), and University of Santiago de Compostela (N = 944), for a total of 4612 individuals. STRSeq data are maintained as GenBank records at the U.S. National Center for Biotechnology Information (NCBI), which participates in a daily data exchange with the DNA DataBank of Japan (DDBJ) and the European Nucleotide Archive (ENA). Each GenBank record contains the observed sequence of a STR region, annotation (“bracketing”) of the repeat region and flanking region polymorphisms, information regarding the sequencing assay and data quality, and backward compatible length-based allele designation. STRSeq GenBank records are organized within a BioProject at NCBI (https://www.ncbi.nlm.nih.gov/bioproject/380127), which is sub-divided into: commonly used autosomal STRs, alternate autosomal STRs, Y-chromosomal STRs, and X-chromosomal STRs. Each of these categories is further divided into locus-specific BioProjects. The BioProject hierarchy facilitates access to the GenBank records by browsing, BLAST searching, or ftp download. Future plans include user interface tools at strseq.nist.gov, a pathway for submission of additional allele records by laboratories performing population sample sequencing and interaction with the STRidER web portal for quality control (http://strider.online).

This report summarizes topics discussed at the STR sequence nomenclature meeting hosted by the STRAND Working Group in April 2019. Invited attendees for this meeting included researchers known-to-us to be developing STR sequence-based nomenclature schemata, scientific representatives from vendors developing STR sequence bioinformatic methods, DNA intelligence database curators, and academic experts in STR genomics. The goal of this meeting was to provide a forum for individuals developing nomenclature schemata to present and discuss their ideas, encouraging mutual awareness, identification of differences in approaches, opposing aspects, and opportunities for parallelization while some approaches are still under development.

Sequence data was analyzed from the flanking and repeat regions of 22 autosomal STR loci in 183 population samples. The flanking regions of the loci sequenced in this data set can be divided into six categories, based on the types of polymorphisms they contain: (1) multiple polymorphisms in haplotype, (2) "old" single polymorphisms, (3) population or allele specific polymorphisms, (4) polymorphisms associated with sequence variants, (5) rare polymorphisms, and (6) no polymorphisms. These results provide an indication of which loci are expected to gain in areas such as allelic diversity and ancestry information by including flanking regions in STR sequence analysis.

The development of next generation sequencing (NGS) technologies creates the potential for changing the method by which the forensic science community genotypes short tandem repeat (STR) loci. While the capabilities of NGS are promising, moving from current capillary electrophoresis (CE) methods would require new guidelines to be established and a new understanding of artifacts that may arise with the use of NGS. Stutter has been well characterized for CE technologies; however, NGS workflows may use different polymerases and amplification approaches, which could alter the appearance of this artifact. Stutter is most commonly seen in the n -4 position in CE data, but may be observed more rarely in the n +4 and n -8 positions. NGS data frequently contains detectable sequences consistent with stutter at the n +4 and n -8 positions, and may even contain stutter at the n -12 position for some loci. It is possible that these alternate types of stutter events occur at similar levels in CE workflows and go undetected due to the analytical threshold employed or because the artifacts do not exceed the background noise. Comparing stutter events in NGS data to what has been observed by CE will improve our understanding of the effects of library preparation and sequencing. Characterizing stutter events by sequence will contribute to the development of guidelines and facilitate implementation of NGS technology. Further, determining stutter ratios for each isoallele would allow for individual sequence thresholds to be set, which could then be used to improve mixture interpretation models.

The DNA Commission of the International Society for Forensic Genetics (ISFG) is reviewing factors that need to be considered ahead of the adoption by the forensic community of short tandem repeat (STR) genotyping by massively parallel sequencing (MPS) technologies. MPS produces sequence data that provide a precise description of the repeat allele structure of a STR marker and variants that may reside in the flanking areas of the repeat region. When a STR contains a complex arrangement of repeat motifs, the level of genetic polymorphism revealed by the sequence data can increase substantially. As repeat structures can be complex and include substitutions, insertions, deletions, variable tandem repeat arrangements of multiple nucleotide motifs, and flanking region SNPs, established capillary electrophoresis (CE) allele descriptions must be supplemented by a new system of STR allele nomenclature, which retains backward compatibility with the CE data that currently populate national DNA databases and that will continue to be produced for the coming years. Thus, there is a pressing need to produce a standardized framework for describing complex sequences that enable comparison with currently used repeat allele nomenclature derived from conventional CE systems. It is important to discern three levels of information in hierarchical order (i) the sequence, (ii) the alignment, and (iii) the nomenclature of STR sequence data. We propose a sequence (text) string format the minimal requirement of data storage that laboratories should follow when adopting MPS of STRs. We further discuss the variant annotation and sequence comparison framework necessary to maintain compatibility among established and future data. This system must be easy to use and interpret by the DNA specialist, based on a universally accessible genome assembly, and in place before the uptake of MPS by the general forensic community starts to generate sequence data on a large scale. While the established nomenclature for CE-based STR analysis will remain unchanged in the future, the nomenclature of sequence-based STR genotypes will need to follow updated rules and be generated by expert systems that translate MPS sequences to match CE conventions in order to guarantee compatibility between the different generations of STR data.

In the process of establishing short tandem repeat (STR) sequence variant nomenclature guidelines in anticipation of expanded forensic multiplexes for massively parallel sequencing (MPS), it was discovered that the STR D5S2500 has multiple positions and genomic characteristics reported. This ambiguity is because the marker named D5S2500 consists of two different microsatellites forming separate components in the capillary electrophoresis multiplexes of Qiagen’s HDplex (Hilden, Germany) and AGCU ScienTech’s non-CODIS STR 21plex (Wuxi, Jiangsu, China). This study outlines the genomic details used to identify each microsatellite and reveals the D5S2500 marker in HDplex has the correctly assigned STR name, while the D5S2500 marker in the AGCU 21plex, closely positioned a further 1643 nucleotides in the human reference sequence, is an unnamed microsatellite. The fact that the D5S2500 marker has existed as two distinct STR loci undetected for almost ten years, even with reported discordant genotypes for the standard control DNA, underlines the need for careful scrutiny of the genomic properties of forensic STRs, as they become adapted for sequence analysis with MPS systems. We make the recommendation that precise chromosome location data must be reported for any forensic marker under development but not in common use, so that the genomic characteristics of the locus are validated to the same level of accuracy as its allelic variation and forensic performance. To clearly differentiate each microsatellite, we propose the name D5S2800 be used to identify the Chromosome-5 STR in the AGCU 21plex.

The NIST U.S. Population Sample Set consists of 1036 unrelated individuals. There are four population groups represented: African American (n=342), Asian (n=97), Caucasian (n=361), and Hispanic (n=236). These samples have been analyzed using next generation sequencing technology targeting important STR sequences commonly used for human identification. The analysis of SE33 included in this data set required a customized bioinformatic approach to identify and process the allelic information. The locus SE33 is one of the most polymorphic markers used by the forensic community [1]. SE33 is a highly variable locus by length and sequencing has resulted in a four-fold increase in the number of observed alleles. The NIST Population Sample Set has an observed range of 6.3–36 tetranucleotide repeats [2]. It has 52 unique alleles by length and 264 unique alleles by sequence. Analysis of this data set shows 100% concordance with length based methods when flanking sequence is considered. The different categories (patterns) of repeat motifs revealed will be illustrated.

Forensic DNA casework samples are often of insufficient quantity or quality to generate full profiles by conventional DNA typing methods. Polymerase chain reaction (PCR) amplification of short tandem repeat (STR) loci is inherently limited in samples containing degraded DNA, as the cumulative size of repeat regions, primer binding regions, and flanking sequence is necessarily larger than the PCR template. Additionally, traditional capillary electrophoresis (CE) assay design further inherently limits shortening amplicons because the markers must be separated by size. Non-traditional markers, such as single nucleotide polymorphisms (SNPs) and insertion deletion polymorphisms (InDels), may yield more information from challenging samples due to their smaller amplicon size. In this study, the performance of a next generation sequencing (NGS) SNP assay and CE-based STR, mini-STR, and InDel assays was evaluated with a series of fragmented, size-selected samples. Information obtained from the NGS SNP assay exhibited higher overall inverse random match probability (1/RMP) values compared to the CE-based typing assays, with particular benefit for fragment sizes ≤ 150 base pairs (bp). The InDel, mini-STR, and NGS SNP assays all had similar percentages of loci with reportable alleles at this level of degradation; however, the relatively fewer number of loci in the InDel and mini-STR assays results in the NGS SNP assay having at least nine orders of magnitude higher 1/RMP values. In addition, the NGS SNP assay and three CE-based assays (two STR and one InDel assay) were tested using a dilution series consisting of 0.5 ng, 0.1 ng, and 0.05 ng non-degraded DNA. All tested assays showed similar percentages of loci with reportable alleles at these levels of input DNA; however, due to the larger number of loci, the NGS SNP assay and the larger of the two tested CE-based STR assays both resulted in considerably higher 1/RMP values than the other assays. These results indicate the potential advantage of NGS SNP assays for forensic analysis of degraded DNA samples.

The advent and adoption of next generation sequencing (NGS) is enabling analysis of single nucleotide polymorphisms (SNPs) at an unprecedented scale, limited primarily by multiplexing during the PCR amplification based enrichment step used for forensic applications. Since only a single nucleotide is assayed, PCR primers may be designed to generate small amplicons, making SNP markers well-suited to forensic DNA typing. Carefully selected panels of SNP markers have been previously established for forensic applications such as one-to-one matching, estimating biogeographical ancestry, and predicting externally visible phenotype [1–6]. To support the implementation of SNPs in forensic DNA analysis, NIST has examined the HID-Ion AmpliSeq Identity Panel and the HID-Ion AmpliSeq Ancestry Panel for the Ion Torrent Personal Genome Machine (PGM). In total, over 289 SNP markers have been typed. NIST intends to use a strategy combining NGS on orthogonal platforms and Sanger sequencing for characterizing the SNP markers for varying levels of confidence. The outcome will be to report only the SNP allele calls, analogous to the mitochondrial sequence variants in NIST Standard Reference Material (SRM) 2392, and not the subsequent application of the information (e.g. prediction of ancestry or phenotype).