A sequence-based 74plex microhaplotype assay for analysis of forensic DNA mixtures

Deconvoluting multi-person biological mixtures and accurate characterization and identification of separated contributors using non-targeted single-cell DNA sequencing

The genetic characterization and identification of individuals who contributed to biological mixtures are complex and mostly unresolved tasks. These tasks are relevant in various fields, particularly in forensic investigations, which frequently encounters crime scene stains generated by more than one person. Currently, forensic mixture deconvolution is mostly performed subsequent to forensic DNA profiling at the level of the mixed DNA profiles, which comes with several limitations. Some previous studies attempted at separating single cells prior to forensic DNA profiling. However, these approaches are biased at selection of the cells and, due to their targeted DNA analysis on low template DNA, provide incomplete and unreliable forensic DNA profiles. We recently demonstrated the feasibility of performing mixture deconvolution prior to forensic DNA profiling through the utilization of a non-targeted single-cell transcriptome sequencing (scRNA-seq). In addition to individual-specific mixture deconvolution, this approach also allowed accurate characterisation of biological sex, biogeographic ancestry and individual identification of the separated mixture contributors. However, RNA has the forensic disadvantage of being prone to degradation, and sequencing RNA - focussing on coding regions - limits the number of single nucleotide polymorphisms (SNPs) utilized for genetic mixture deconvolution, characterization, and identification. These limitations can be overcome by performing single-cell sequencing on the level of DNA instead of RNA. Here, for the first time, we applied non-targeted single-cell DNA sequencing (scDNA-seq) by applying the scATAC-seq (Assay for Transposase-Accessible Chromatin with sequencing) technique to address the challenges of mixture deconvolution in the forensic context. We demonstrated that scATAC-seq, together with our recently developed De-goulash data analysis pipeline, is capable of deconvoluting complex blood mixtures of five individuals from both sexes with varying biogeographic ancestries. We further showed that our approach achieved correct genetic characterization of the biological sex and the biogeographic ancestry of each of the separated mixture contributors and established their identity. Furthermore, by analysing in-silico generated scATAC-seq data mixtures, we demonstrated successful individual-specific mixture deconvolution of i) highly complex mixtures of 11 individuals, ii) balanced mixtures containing as few as 20 cells (10 per each individual), and iii) imbalanced mixtures with a ratio as low as 1:80. Overall, our proof-of-principle study demonstrates the general feasibility of scDNA-seq in general, and scATAC-seq in particular, for mixture deconvolution, genetic characterization and individual identification of the separated mixture contributors. Furthermore, it shows that compared to scRNA-seq, scDNA-seq detects more SNPs from fewer cells, providing higher sensitivity, that is valuable in forensic genetics.

MHBase: A comprehensive database of short microhaplotypes for advancing forensic genetic analysis

Microhaplotypes (MHs) were first recommended by Prof. Kidd for use in forensics because they can improve human identification, kinship analysis, mixture deconvolution, and ancestry prediction. Since their introduction, extensive research has demonstrated the advantages of MHs in forensic applications and provided useful data for different populations. Currently, two databases, ALFRED (ALlele FREquency Database) and MicroHapDB (MicroHaplotype DataBase), house the published MH information and population data. We previously constructed a single nucleotide polymorphism SNP-SNP MH database (D-SNPsDB) of MHs within 50 bp on the whole human genome for 26 populations integrating basic data such as physical genome positions, mapping of variant identifiers (rsIDs), allele frequencies, and basic variant information. Building upon the previous research, we further selected MHs containing at least two variants (SNPs and/or insertions/deletions [InDels]) within a short DNA fragment (≤ 50 bp) in 26 populations based on the 1000 Genomes Project dataset (Phase 3) to construct a more comprehensive database. Subsequently, we established a user-friendly website that allows users to search the MH database (MHBase) based on their research objectives and study population to find suitable loci and provides other functions such as querying reported loci, performing online calculations using the PHASE software, and calculating ancestral-related parameters. The loci in the database are classified as SNP-based MHs, which include only SNPs, and InDel-including MHs, which contain at least one InDel. Here, we provide a detailed overview of the MHBase and an analysis of shared loci at the global and continental levels, ancestral markers, the genetic distance within loci, and mapping with the genome annotation file. The website is an accessible and useful tool for researchers engaged in marker discovery, population studies, assay development, and panel design.

Simultaneous sequencing of 102 Y-STRs on Ion Torrent ™ GeneStudio ™ S5 System

The Precision ID NGS System from Thermo Fisher Scientific is a mainstream next-generation sequencing (NGS) platform used in forensic laboratories to detect almost all commonly used forensic markers, except for Y-chromosomal short tandem repeats (Y-STRs). This study aimed to: 1) develop a Y-STR panel compatible with the automatic workflow of the NGS system using Ion AmpliSeq Technology, 2) evaluate the panel performance following the SWGDAM guidelines, and 3) explore the possibility of using a combination workflow to detect autosomal STRs and Y-STRs (AY-STR NGS workflow). The GrandFiler Y-STR Panel was successfully designed using the 'separating' and 'merging' strategies, including 102 Y-STRs and Amelogenin with an average amplicon length of 133 bp. It is a mega Y-STR multiplex system in which up to 16 samples can be sequenced simultaneously on an Ion 530 ™ Chip. Developmental validation studies of the performance of the NGS platform, species specificity, reproducibility, concordance, sensitivity, degraded samples, case-type samples, and mixtures were conducted to unequivocally determine whether the GrandFiler Y-STR Panel is suitable for real scenarios. The newly developed Y-STR panel showed compelling run metrics and NGS performance, including 92.47% bases with ≥ Q20, 91.80% effective reads, 2106 × depth of coverage (DoC), and 97.09% inter-locus balance. Additionally, it showed high specificity for human males and 99.40% methodological and bioinformatical concordance, generated complete profiles at ≥ 0.1 ng input DNA, and recovered more genetic information from severely degraded and diverse case samples. Although the outcome when used on mixtures was not as expected, more genetic information was obtained compared to that from capillary electrophoresis (CE) methods. The AY-STR NGS workflow was established by combining the GrandFiler Y-STR Panel with the Precision ID GlobalFiler ™ NGS STR Panel v2 at a 2:1 concentration ratio. The combination workflow on NGS performance, reproducibility, concordance, and sensitivity was as stable as the single Y-STR NGS workflow, providing more options for forensic scientists when dealing with different case scenarios. Overall, the GrandFiler Y-STR Panel was confirmed as the first to effectively detect a large number of Y-STR markers on the Precision ID NGS System, which is compatible with 51 Y-STRs in commercial CE kits and 51 Y-STRs in commercial NGS kits and the STRBase. The panel is as robust, reliable, and sensitive as current CE/NGS kits, and is suitable for solving real cases, especially for severely degraded samples (degradation index > 10).

A preliminary study on identification of the blood donor in a body fluid mixture using a novel compound genetic marker blood-specific methylation-microhaplotype

Blood-containing mixtures are frequently encountered at crime scenes involving violence and murder. However, the presence of blood, and the association of blood with a specific donor within these mixtures present significant challenges in forensic analysis. In light of these challenges, this study sought to address these issues by leveraging blood-specific methylation sites and closely linked microhaplotype sites, proposing a novel composite genetic marker known as "blood-specific methylation-microhaplotype". This marker was designed to the detection of blood and the determination of blood donor within blood-containing mixtures. According to the selection criteria mentioned in the Materials and Methods section, we selected 10 blood-specific methylation-microhaplotype loci for inclusion in this study. Among these loci, eight exhibited blood-specific hypomethylation, while the remaining two displayed blood-specific hypermethylation. Based on data obtained from 124 individual samples in our study, the combined discrimination power (CPD) of these 10 successfully sequenced loci was 0.999999298. The sample allele methylation rate (Ram) was obtained from massive parallel sequencing (MPS), which was defined as the proportion of methylated reads to the total clustered reads that were genotyped to a specific allele. To develop an allele type classification model capable of identifying the presence of blood and the blood donor, we used the Random Forest algorithm. This model was trained and evaluated using the Ram distribution of individual samples and the Ram distribution of simulated shared alleles. Subsequently, we applied the developed allele type classification model to predict alleles within actual mixtures, trying to exclude non-blood-specific alleles, ultimately allowing us to identify the presence of blood and the blood donor in the blood-containing mixtures. Our findings demonstrate that these blood-specific methylation-microhaplotype loci have the capability to not only detect the presence of blood but also accurately associate blood with the true donor in blood-containing mixtures with the mixing ratios of 1:29, 1:19, 1:9, 1:4, 1:2, 2:1, 7:1, 8:1, 31:1 and 36:1 (blood:non-blood) by DNA mixture interpretation methods. In addition, the presence of blood and the true blood donor could be identified in a mixture containing four body fluids (blood:vaginal fluid:semen:saliva = 1:1:1:1). It is important to note that while these loci exhibit great potential, the impact of allele dropouts and alleles misidentification must be considered when interpreting the results. This is a preliminary study utilising blood-specific methylation-microhaplotype as a complementary tool to other well-established genetic markers (STR, SNP, microhaplotype, etc.) for the analysis in blood-containing mixtures.

Developmental validation of a custom-designed Multi-InDel panel: A five-dye multiplex amplification system for challenging DNA samples

The continual investigation of novel genetic markers has yielded promising solutions for addressing the challenges encountered in forensic DNA analysis. In this study, we have introduced a custom-designed panel capable of simultaneously amplifying 41 novel Multi-insertion/deletion (Multi-InDel) markers and an amelogenin locus using the capillary electrophoresis platform. Through a developmental validation study conducted in accordance with guidelines recommended by the Scientific Working Group on DNA Analysis Methods, we demonstrated that the new Multi-InDel system exhibited the sensitivity to produce reliable genotyping profiles with as little as 62.5 pg of template DNA. Accurate and complete genotyping profiles could be obtained even in the presence of specific concentrations of PCR inhibitors. Furthermore, the maximum amplicon size for this system was limited to under 220 bp in the genotyping profile, resulting in its superior efficiency compared to commercially available short tandem repeat kits for both naturally and artificially degraded samples. In the context of mixed DNA analysis, the Multi-InDel system was proved informative in the identification of two-person DNA mixture, even when the template DNA of the minor contributor was as low as 50 pg. In conclusion, a series of performance evaluation studies have provided compelling evidence that the new Multi-InDel system holds promise as a valuable tool for forensic DNA analysis.

Improving DNA mixtures analysis using compound markers composed of InDels and SNPs screened from the whole genome with next-generation sequencing

Next-generation sequencing (NGS) allows for better identification of insertion and deletion polymorphisms (InDels) and their combination with adjacent single nucleotide polymorphisms (SNPs) to form compound markers. These markers can improve the polymorphism of microhaplotypes (MHs) within the same length range, and thus, boost the efficiency of DNA mixture analysis. In this study, we screened InDels and SNPs across the whole genome and selected highly polymorphic markers composed of InDels and/or SNPs within 300 bp. Further, we successfully developed and evaluated an NGS-based panel comprising 55 loci, of which 24 were composed of both SNPs and InDels. Analysis of 124 unrelated Southern Han Chinese revealed an average effective number of alleles (Ae ) of 7.52 for this panel. The cumulative power of discrimination and cumulative probability of exclusion values of the 55 loci were 1-2.37 × 10-73 and 1-1.19 × 10-28 , respectively. Additionally, this panel exhibited high allele detection rates of over 97% in each of the 21 artificial mixtures involving from two to six contributors at different mixing ratios. We used EuroForMix to calculate the likelihood ratio (LR) and evaluate the evidence strength provided by this panel, and it could assess evidence strength with LR, distinguishing real and noncontributors. In conclusion, our panel holds great potential for detecting and analyzing DNA mixtures in forensic applications, with the capability to enhance routine mixture analysis.

Using simulated microhaplotype genotyping data to evaluate the value of machine learning algorithms for inferring DNA mixture contributor numbers

Inferring the number of contributors (NoC) is a crucial step in interpreting DNA mixtures, as it directly affects the accuracy of the likelihood ratio calculation and the assessment of evidence strength. However, obtaining the correct NoC in complex DNA mixtures remains challenging due to the high degree of allele sharing and dropout. This study aimed to analyze the impact of allele sharing and dropout on NoC inference in complex DNA mixtures when using microhaplotypes (MH). The effectiveness and value of highly polymorphic MH for NoC inference in complex DNA mixtures were evaluated through comparing the performance of three NoC inference methods, including maximum allele count (MAC) method, maximum likelihood estimation (MLE) method, and random forest classification (RFC) algorithm. In this study, we selected the top 100 most polymorphic MH from the Southern Han Chinese (CHS) population, and simulated over 40 million complex DNA mixture profiles with the NoC ranging from 2 to 8. These profiles involve unrelated individuals (RM type) and related pairs of individuals, including parent-offspring pairs (PO type), full-sibling pairs (FS type), and second-degree kinship pairs (SE type). Our results indicated that how the number of detected alleles in DNA mixture profiles varied with the markers' polymorphism, kinship's involvement, NoC, and dropout settings. Across different types of DNA mixtures, the MAC and MLE methods performed best in the RM type, followed by SE, FS, and PO types, while RFC models showed the best performance in the PO type, followed by RM, SE, and FS types. The recall of all three methods for NoC inference were decreased as the NoC and dropout levels increased. Furthermore, the MLE method performed better at low NoC, whereas RFC models excelled at high NoC and/or high dropout levels, regardless of the availability of a priori information about related pairs of individuals in DNA mixtures. However, the RFC models which considered the aforementioned priori information and were trained specifically on each type of DNA mixture profiles, outperformed RFC_ALL model that did not consider such information. Finally, we provided recommendations for model building when applying machine learning algorithms to NoC inference.

Performance of a 74-Microhaplotype Assay in Kinship Analyses

Microhaplotypes (MHs) consisting of multiple SNPs and indels on short stretches of DNA are new and interesting loci for forensic genetic investigations. In this study, we analysed 74 previously defined MHs in two of the populations that our laboratory provides with forensic genetic services, Danes and Greenlanders. In addition to the 229 SNPs that originally made up the 74 MHs, 66 SNPs and 3 indels were identified in the two populations, and 45 of these variants were included in new definitions of the MHs, whereas 24 SNPs were considered rare and of little value for case work. The average effective number of alleles (Ae) was 3.2, 3.0, and 2.6 in Danes, West Greenlanders, and East Greenlanders, respectively. High levels of linkage disequilibrium were observed in East Greenlanders, which reflects the characteristics of this population that has a small size, and signs of admixture and substructure. Pairwise kinship simulations of full siblings, half-siblings, first cousins, and unrelated individuals were performed using allele frequencies from MHs, STRs and SNPs from Danish and Greenlandic populations. The MH panel outperformed the currently used STR and SNP marker sets and was able to differentiate siblings from unrelated individuals with a 0% false positive rate and a 1.1% false negative rate using an LR threshold of 10,000 in the Danish population. However, the panel was not able to differentiate half-siblings or first cousins from unrelated individuals. The results generated in this study will be used to implement MHs as investigative markers for relationship testing in our laboratory.

Adapting an established Ampliseq microhaplotype panel to nanopore sequencing through direct PCR

We have adapted an established Ampliseq microhaplotype panel for nanopore sequencing with the Oxford Nanopore Technologies (ONT) system, as a cost-effective and highly scalable solution for forensic genetics applications. For this purpose, we designed a protocol combining direct PCR amplification from unextracted DNA with ONT library construction and sequencing using the MinION device and workflow. The analysis of reference samples at input amounts of 5-10 ng of DNA demonstrates stable coverage patterns, allele balance, and strand bias, reaching profile completeness and concordance rates of ∼95%. Similar levels were achieved when using direct-PCR from blood, buccal and semen swabs. Dilution series results indicate sensitivity is maintained down to 250 pg of input DNA, and informative profiles are produced down to 62.5 pg. Finally, we demonstrated the forensic utility of the nanopore workflow by analyzing two third degree pedigrees that showed low likelihood ratio values after the analysis of an extended panel of 38 STRs, achieving likelihood ratios 2-3 orders of magnitude higher when testing with the MinION-based haplotype data.

Massively parallel sequencing of 74 microhaplotypes and forensic characteristics in three Chinese Sino-Tibetan populations

Microhaplotype (MH), as an emerging type of forensic genetic marker in recent years, has the potential to support multiple forensic applications, especially for mixture deconvolution and biogeographic ancestry inference. Herein, we investigated the genotype data of 74 MHs included in a novel MH panel, the Ion AmpliSeq MH-74 Plex Microhaplotype Research Panel, in three Chinese Sino-Tibetan populations (Han, Tibetan, and Yi) using the Ion Torrent semiconductor sequencing. The sequencing performance, allele frequencies, effective number of alleles (Ae), informativeness (In), and forensic parameters were subsequently estimated and calculated. In addition, principal component analysis (PCA) and structure analysis were performed to explore the population relationships among the three populations and the ancestry component distribution. Overall, this novel MH panel is robust and reliable, and has an excellent sequencing performance. The Ae values ranged from 1.0126 to 7.0855 across all samples, and 75.68 % of MHs had Ae values >2.0000. Allele frequencies at some loci varied considerably among the three studied populations, and the mean In value was 0.0195. Moreover, the genetic affinity between Tibetans and Yis was closer than that between Tibetans and Hans. The aforementioned results suggest that the Ion AmpliSeq MH-74 Plex Microhaplotype Research Panel is highly polymorphic in three investigated populations and could be used as an effective tool for human forensics. Although these 74 MHs have demonstrated the competency in continental population stratification, a higher resolution for distinguishing intracontinental subpopulations and a more comprehensive database with sufficient reference population data still remain to be accomplished.

Evaluation of microhaplotype panels for complex kinship analysis using massively parallel sequencing

In recent years, microhaplotypes (MHs) have become a research hotspot within the field of forensic genetics. Traditional MHs contain only SNPs that are closely linked within short fragments. Herein, we broaden the concept of general MHs to include short InDels. Complex kinship identification plays an important role in disaster victim identification and criminal investigations. For distant relatives (e.g., 3rd-degree), many genetic markers are required to enhance power of kinship testing. We performed genome-wide screening for new MH markers composed of two or more variants (InDel or SNP) within 220 bp based on the Chinese Southern Han from the 1000 Genomes Project. An NGS-based 67plex MH panel (Panel B) was successfully developed, and 124 unrelated individual samples were sequenced to obtain population genetic data, including alleles and allele frequencies. Of the 67 genetic markers, 65 MHs were, as far as we know, newly discovered, and 32 MHs had effective number of allele (A_e) values greater than 5.0. The average A_e and heterozygosity of the panel were 5.34 and 0.7352, respectively. Next, 53 MHs from a previous study were collected as Panel A (average A_e of 7.43), and Panel C with 87 MHs (average A_e of 7.02) was formed by combining Panels A and B. We investigated the utility of these three panels in kinship analysis (parent-child, full siblings, 2nd-degree, 3rd-degree, 4th-degree, and 5th-degree relatives), with Panel C exhibiting better performance than the two other panels. Panel C was able to separate parent-child, full-sibling, and 2nd-degree relative duos from unrelated controls in real pedigree data, with a small false testing level (FTL) of 0.11% in simulated 2nd-degree duos. For more distant relationships, the FTL was much higher: 8.99% for 3rd-degree, 35.46% for 4th-degree, and 61.55% for 5th-degree. When a carefully chosen extra relative was known, this may enhance the testing power for distant kinship analysis. Two twins from the Q family (2-5 and 2-7) and W family (3-18 and 3-19) shared the same genotypes in all tested MHs, which led to the incorrect conclusion that an uncle-nephew duo was classified as a parent-child duo. In addition, Panel C showed great capacity for excluding close relatives (2nd-degree and 3rd-degree relatives) during paternity tests. Among 18,246 real and 10,000 simulated unrelated pairs, none were misinterpreted as a relative within 2nd-degree at a log₁₀(LR) cutoff of 4. The panels presented herein could provide supplementary power for the analysis of complex kinship.

An MPS-Based 50plex Microhaplotype Assay for Forensic DNA Analysis

Microhaplotypes (MHs) are widely accepted as powerful markers in forensic studies. They have the advantage of both short tandem repeats (STRs) and single nucleotide polymorphisms (SNPs), with no stutter and amplification bias, short fragments and amplicons, low mutation and recombination rates, and high polymorphisms. In this study, we constructed a panel of 50 MHs that are distributed on 21 chromosomes and analyzed them using the Multiseq multiple polymerase chain reaction (multi-PCR) targeted capture sequencing protocol based on the massively parallel sequencing (MPS) platform. The sizes of markers and amplicons ranged between 11–81 bp and 123–198 bp, respectively. The sensitivity was 0.25 ng, and the calling results were consistent with Sanger sequencing and the Integrative Genomics Viewer (IGV). It showed measurable polymorphism among sequenced 137 Southwest Chinese Han individuals. No significant deviations in the Hardy–Weinberg equilibrium (HWE) and linkage disequilibrium (LD) were found at all MHs after Bonferroni correction. Furthermore, the specificity was 1:40 for simulated two-person mixtures, and the detection rates of highly degraded single samples and mixtures were 100% and 93–100%, respectively. Moreover, animal DNA testing was incomplete and low depth. Overall, our MPS-based 50-plex MH panel is a powerful forensic tool that provides a strong supplement and enhancement for some existing panels.

Systematically exploring the performance of a self-developed Multi-InDel system in forensic identification, ancestry inference and genetic structure analysis of Chinese Manchu and Mongolian groups

The insertion/deletion (InDel) polymorphism has promising applications in forensic DNA analysis. However, the insufficient forensic efficiencies of the present InDel-based systems restrict their applications in parentage testing, due to the lower genetic polymorphism of the biallelic InDel locus and the limited number of InDel loci in a multiplex amplification system. Here, we introduced an in-house developed system which contained 41 polymorphic Multi-InDel markers (equivalent to 82 InDels in total), to serve as an efficient and reliable tool for different forensic applications in the Manchu and Mongolian groups. We demonstrated that the new system exhibited potential efficiencies for personal identification, parentage testing, two-person DNA mixture interpretation and ancestry inference of intercontinental populations. Meanwhile, we explored the genetic backgrounds of the Manchu and Mongolian groups by conducting a series of population genetic analyses. We showed that the Manchu and Mongolian groups shared closer genetic relationships with East Asian populations, especially Han Chinese populations in northern China. Moreover, more similar genetic compositions were detected between the Manchu group and the northern Han populations in this study, suggesting that the Manchu group had higher genetic affinities with northern Han populations than the Mongolian group. Overall. this study provided the necessary evidence that these Multi-InDel genetic markers could play an important role in forensic applications.

Development and evaluation of a novel panel containing 188 microhaplotypes for 2nd-degree kinship testing in the Hebei Han population

Distant kinship identification is one of the critical problems in forensic genetics. As a new type of genetic marker defined and discussed in the last decade, the microhaplotype (MH) has drawn much attention in such identification owing to its specific advantages to traditional short tandem repeat (STR) or single nucleotide polymorphism (SNP) markers. In this study, MH markers were screened step by step from the 1000 Genomes Project database, and a novel multiplex panel containing 188 MHs (in which 181 are reported the first time, while 1 was reported in a previous study and the other 6 have partial overlaps with known markers) was constructed for application in 2nd- and 3rd-degree kinship identification. Along with the construction, a novel MH nomenclature was proposed, in which the SNP position information they contained was taken into account to eliminate the possibility that the same locus was named differently interlaboratory. After a series of evaluations, the panel was shown to have good sequencing accuracy, high sensitivity, species specificity, and resistance to anti-PCR inhibitors or degradation. Population data of the 188 MHs were calculated based on the genetic information of 221 unrelated Hebei Han individuals, and the effective number of alleles (Ae) ranged from 2.0925 to 8.2634 (with an average of 2.9267). For the whole system, the cumulative matching probability (CMP), the cumulative power of exclusion in paternity testing of duos (CPEduo) and that of trios (CPEtrio) reached 2.8422 × 10^-137, 1-1.3109 × 10^-21, and 1-2.8975 × 10^-39, respectively, indicating that this panel was satisfactory for individual identification and paternity testing. Then, the efficiency of the 188 MHs in 2nd- and 3rd-degree kinship testing was studied based on 30 extended families consisting of 179 2nd-degree and 121 3rd-degree relatives, as well as simulations of 0.5 million pairs of those two kinships. The results showed that clear opinions would be given in 83.36% of 2nd-degree identifications with a false rate less than 10^-5, when the confirming and excluding thresholds of cumulative likelihood ratio (CLR) were set as 10⁴ and 10^-4, respectively. This panel is still not sufficient to solve the problem of 3rd-degree kinship identification alone, and approximately 300 or 870 MH loci would be needed in 2nd- or 3rd-degree kinship identification, respectively, to achieve a system efficiency not less than 0.99 with such a threshold set; such necessary numbers would be used only as a reference in further research.

Evaluation of a SNP-STR haplotype panel for forensic genotype imputation

Short tandem repeat polymorphism (STR)-based individual identification is a popular and reliable method in many forensic applications. However, STRs still frequently fail to find any matched records. In such cases, if known STRs could provide more information, it would be very helpful to solve specific problems. Genotype imputation has long been used in the study of single nucleotide polymorphisms (SNPs) and has recently been introduced into forensic fields. The idea is that, through a reference haplotype panel containing SNPs and STRs, we can obtain unknown genetic information through genotype imputation based on known STR or SNP genotypes. Several recent studies have already demonstrated this exciting idea, and a 1000 Genomes SNP-STR haplotype panel has also been released. To further study the performance of genotype imputation in forensic fields, we collected STR, microhaplotype (MH) and SNP array genotypes from Chinese Han population individuals and then performed genotype imputation analysis based on the released reference panel. As a result, the average locus imputation accuracy was ∼83 % (or ∼70 %) when SNPs in the SNP array (or MH SNPs) were imputed from STRs, and was ∼30 % when highly polymorphic markers (STRs and MHs) were imputed from each other. When STRs were imputed from SNP array, the average locus imputation accuracy increased to ∼48 %. After analyzing the match scores between real STRs and the STRs imputed from SNPs, ∼80 % of studied STR records can be connected to corresponding SNP records, which may help for individual identification. Our results indicate that genotype imputation has great potential for forensic applications.

A sequence-based 163plex microhaplotype assay for forensic DNA analysis

Novel genetic marker microhaplotype has led to an upsurge in forensic genetic research. This study established a 163 microhaplotype (MH) multiplex assay based on next-generation sequencing (NGS) and evaluated the assay’s performance and applicability. Our results showed that the 163 MH assay was accurate, repeatable and reliable, and could distinguish between African, European-American, Southern Asia and Eastern Asia populations. Among the 163 MH makers, 48 MHs with Ae > 3.0 in China Eastern Han were selected and confirmed to be highly polymorphic, with a combined power of discrimination of 1–8.26 × 10–44 and the combined power of exclusion in duos and trios of 1–1.26 × 10–8 and 1–8.27 × 10–16, respectively. Moreover, the mixture study demonstrated the realizability of the MHs in deconvoluting mixtures with different proportions of two to five-person. In conclusion, our findings support the use of this MH assay for ancestry inference, human identification, paternity testing and mixture deconvolution in forensic research.

Applications of massively parallel sequencing in forensic genetics

Massively parallel sequencing, also referred to as next-generation sequencing, has positively changed DNA analysis, allowing further advances in genetics. Its capability of dealing with low quantity/damaged samples makes it an interesting instrument for forensics. The main advantage of MPS is the possibility of analyzing simultaneously thousands of genetic markers, generating high-resolution data. Its detailed sequence information allowed the discovery of variations in core forensic short tandem repeat loci, as well as the identification of previous unknown polymorphisms. Furthermore, different types of markers can be sequenced in a single run, enabling the emergence of DIP-STRs, SNP-STR haplotypes, and microhaplotypes, which can be very useful in mixture deconvolution cases. In addition, the multiplex analysis of different single nucleotide polymorphisms can provide valuable information about identity, biogeographic ancestry, paternity, or phenotype. DNA methylation patterns, mitochondrial DNA, mRNA, and microRNA profiling can also be analyzed for different purposes, such as age inference, maternal lineage analysis, body-fluid identification, and monozygotic twin discrimination. MPS technology also empowers the study of metagenomics, which analyzes genetic material from a microbial community to obtain information about individual identification, post-mortem interval estimation, geolocation inference, and substrate analysis. This review aims to discuss the main applications of MPS in forensic genetics.

Application of a custom haplotype caller to analyze sequence-based data of 56 microhaplotypes

Microhaplotypes (microhaps) are recently introduced markers that aim to complement the limitations of conventional forensic markers such as short tandem repeats (STRs) and single nucleotide polymorphisms (SNPs). With the potential of microhaps in forensics becoming clearer through massively parallel sequencing (MPS), MPS-based studies on microhaps are being actively reported. However, simpler workflow schemes for the generation and analysis of MPS data are still required to facilitate the practical application of MPS in forensics. In this study, we developed an in-house MPS panel that simultaneously amplifies 56 microhaps and a custom haplotype caller, Visual Microhap. The developed tool works on a web browser and provides four analysis options to extract SNP-based haplotypes from sequence-based data obtained by STRait Razor 3.0. To demonstrate the utility of the MPS panel and data analysis workflow scheme, we also analyzed 56 microhaps of 286 samples from four populations (African-American, Caucasian, Hispanic, and Korean). The average effective number of alleles (A_e) for the four groups was 3.45, ranging from 1.74 to 6.98. Forensic statistical parameters showed that this microhap panel is more powerful than conventional autosomal STRs for human identification. Meanwhile, the 56-plex panel mostly comprised microhaps with high Ae; however, the four populations were grossly distinguishable from each other by cluster analysis. Consequently, the developed in-house MPS panel for 56 microhaps and the adopted workflow using open-source tools can increase the utility of microhap MPS in forensic research and practice.

A multipurpose panel of microhaplotypes for use with STR markers in casework

A small panel of highly informative loci that can be genotyped on the same equipment as the standard CODIS short tandem repeat (STR) markers has strong potential for application in forensic casework. Single nucleotide polymorphisms (SNPs) can be typed by a couple of methods on capillary electrophoresis (CE) machines and on sequencers, but the amount of information relative to the laboratory effort has hindered use of SNPs in actual casework. Insertion-deletion markers (InDels) suffer from similar problems. Microhaplotypes (MHs) are much more informative per locus but have similar technical difficulties unless they are typed by massively parallel sequencing (MPS). As forensic labs are acquiring sequencing machines, MHs become more likely to be used in casework, especially if multiplexed with STRs. Here we present the details of a multipurpose panel of 24 MHs with the highest effective number of alleles (Ae) from previous work. An augmented STR panel of 24 loci (20 CODIS markers plus four commonly typed STRs) is also considered. The Ae and ancestry informativeness (In) distributions of these two datasets are compared. The MH panel is shown to have better individualization and population distinction than the augmented CODIS STRs. We note that the 24 MHs should be better for mixture analyses than the STRs. Finally, we suggest that a commercial kit including both the standard CODIS markers and this set of 24 MH would greatly improve the discrimination power over that of current commercial assays.

Evaluation of the MHSeqTyper47 kit for forensically challenging DNA samples

Microhaplotypes have been highly regarded for forensic mixture DNA deconvolution because they do not experience interference from stutters in the same way as short tandem repeat markers, and they tend to be more polymorphic than single nucleotide polymorphism markers. However, forensic microhaplotype kits have not been reported. The MHSeqTyper47 kit genotypes 47 microhaplotype loci. In this study, MiSeq FGx sequencing metrics for MHSeqTyper47 were presented, and the genotyping accuracy of this kit was examined. The sensitivity of MHSeqTyper47 reached 62.5 pg, and full genotyping results were obtained from degraded DNA samples with degradation indexes ≤ 3.00. Full genotypes were obtained in the presence of 100 ng/μL tannin, 50 μM heme, 25 ng/μL humic acid, and 1.25 μg/μL indigo dye. In DNA mixture studies, a minimum of 31 loci of the minor contributor were correctly genotyped at 1:99 or 99:1 mixing ratios, with the cumulative random matching probability of these loci reaching 4.54 × 10^-25. Mixing ratios could be reliably predicted from two-donor DNA mixtures based on the loci with four called alleles. Taken together, these data showed that the MHSeqTyper47 kit was effective for forensically challenging DNA analysis.

State of the Art for Microhaplotypes

In recent years, the number of publications on microhaplotypes has averaged more than a dozen papers annually. Many have contributed to a significant increase in the number of highly polymorphic microhaplotype loci. This increase allows microhaplotypes to be very informative in four main areas of forensic uses of DNA: individualization, ancestry inference, kinship analysis, and mixture deconvolution. The random match Probability (RMP) can be as small as 10−100 for a large panel of microhaplotypes. It is possible to measure the heterozygosity of an MH as the effective number of alleles (Ae). Ae > 7.5 exists for African populations and >4.5 exists for Native American populations for a smaller panel of two dozen selected microhaplotypes. Using STRUCTURE, at least 10 different ancestral clusters can be defined by microhaplotypes. The Ae for a locus is also identical to the Paternity Index (PI), the measure of how informative a locus will be in parentage testing. High Ae loci can also be useful in missing persons cases. Finally, high Ae microhaplotypes allow the near certainty of seeing multiple additional alleles in a mixture of two or more individuals in a DNA sample. In summary, a panel of higher Ae microhaplotypes can outperform the standard CODIS markers.

Forensic Feature Exploration and Comprehensive Genetic Insights Into Yugu Ethnic Minority and Northern Han Population via a Novel NGS-Based Marker Set

The MPS technology has expanded the potential applications of DNA markers and increased the discrimination power of the targeted loci by taking variations in their flanking regions into consideration. Here, a collection of nuclear and extranuclear DNA markers (totally six kinds of nuclear genetic markers and mtDNA hypervariable region variations) were comprehensively and systematically assessed for polymorphism detections, further employed to dissect the population backgrounds in the Yugu ethnic group from Gansu province (Yugu) and Han population from the Inner Mongolia Autonomous Region (NMH) of China. The elevated efficiencies of the marker set in separating full sibling and challenging half sibling determination cases in parentage tests (iiSNPs), as well as predicting ancestry origins of unknown individuals from at least four continental populations (aiSNPs) and providing informative characteristic-related clues for Chinese populations (piSNPs) are highlighted in the present study. To sum up, different sets of DNA markers revealed sufficient effciencies to serve as promising tools in forensic applications. Genetic insights from the perspectives of autosomal DNA, Y chromosomal DNA, and mtDNA variations yielded that the Yugu ethnic group was genetically close related to the Han populations of the northern region. But we admit that more reference populations (like Mongolian, Tibetan, Hui, and Tu) should be incorporated to gain a refined genetic background landscape of the Yugu group in future studies.

Forensic nanopore sequencing of microhaplotype markers using QitanTech's QNome

In recent years, extraordinary progress has been made in genome sequencing technologies, which has led to a decrease in cost and an increase in the diversity of sequenced genomes. Nanopore sequencing is one of the latest genome sequencing technologies. It aims to sequence longer contiguous pieces of DNA, which are essential for resolving structurally complex regions, and provides a new approach for forensic genetics to detect longer markers in real time. To date, multiple studies have been conducted to sequence forensic markers using MinION from Oxford Nanopore Technologies (ONT), and the results indicate that nanopore sequencing holds promise for forensic applications. Qitan Technology (QitanTech) recently launched its first commercial nanopore genome sequencer, QNome. It could achieve a read length of more than 150 kbp, and could generate approximately 500 Mb of data in 8 h. In this pilot study, we explored and validated this alternative nanopore sequencing device for microhaplotype (MH) profiling using a custom set of 15 MH loci. Seventy single-contributor samples were divided into 7 batches, each of which included 10 samples and control DNA 9947A and was sequenced by QNome. MH genotypes generated from QNome were compared to those from Ion Torrent sequencing (Ion S5XL system) to evaluate the accuracy and stability. Twelve samples randomly selected from the last three batches and Control DNA 9947A were also subjected to ONT MinION sequencing (with R9.4 flow cell) for parallel comparison. Based on MHtyper, a bioinformatics workflow developed for automated MH designation, all MH loci can be genotyped and reliably phased using the QNome data, with an overall accuracy of 99.83% (4 errors among 2310 genotypes). Three occurred near or in the region of homopolymer sequences, and one existed within 50 bp of the start of the sequencing reaction. In the last 15 samples (12 individual samples and 3 replicates of control DNA 9947A), two SNPs located at 4-mer homopolymers failed to obtain reliable genotypes on the MinION data. This study shows the potential of state-of-the-art nanopore sequencing methods to analyze forensic MH markers. Given the rapid pace of change, sporadic and nonrepetitive errors presented in this study are expected to be resolved by further developments of nanopore technologies and analysis tools.

Forensic characterization of 124 SNPs in the central Indian population using precision ID Identity Panel through next-generation sequencing

With the advent of next-generation sequencing technology, SNP markers are being explored as a useful alternative to conventional capillary electrophoresis-based STR typing. Low mutation rate and short-sized amplicons are added advantages of SNP markers over the STRs. However, to achieve a sufficient level of discrimination among individuals, a higher number of SNPs need to be characterized simultaneously. Hence, the NGS technique is highly useful to analyze a sufficiently higher number of SNPs simultaneously. Though the technique is in its nascent stage, an attempt has been made to assess its usability in the central Indian population by analyzing 124 SNPs (90 autosomal and 34 Y-chromosome) in 95 individuals. Various quality parameters such as locus balance, locus strand balance, heterozygosity balance, and noise level showed a good quality sequence obtained from the Ion GeneStudio S5 instrument. Obtained frequency of SNP alleles ranged from 0.001 to 0.377 in autosomal SNPs. rs9951171 was found to be the most informative SNP in the studied population with the highest PD and lowest MP value. The cumulative MP of 90 SNPs was found to be 4.76698 × 10^-37. Analysis of 34 Y-chromosome SNPs reveals 11 unique haplogroups in 54 male samples with R1a1 as the most frequent haplogroup found in 22.22% of samples. Interpopulation comparison by FST analysis, PCA plot, and STRUCTURE analysis showed genetic stratification of the studied population suggesting the utility of SNP markers present in the Precision ID Identity Panel for forensic demands of the Indian population.

A novel set of short microhaplotypes based on non-binary SNPs for forensic challenging samples

Short tandem repeats (STRs) are the most widely used genetic markers in forensic application, but they are not ideal genetic markers for the analysis of forensic challenging samples such as highly degraded or unbalanced mixed samples because of their relatively large amplicons and stutter peaks. In this study, we developed a set of short microhaplotypes based on non-binary SNPs with molecular extent sizes no longer than 60 bases and genotyped 100 unrelated individuals from northern Han groups. Our results showed this panel has similar discrimination power to STR kits, as the combined random match probability (CMP) reached 1.396 × 10^-22 and mean effective number of alleles (Ae) was 3.59. The cumulative probability of exclusion for duos (CPE-duos) was 0.999919 and the cumulative probability of exclusion for trios (CPE-trios) was 0.9999999987, suggesting this panel could be applied for forensic personal identification and parentage testing independently. Population differentiation in 26 populations from the 1000 Genomes Project indicated this panel could distinguish populations from Africa, East Asia, South Asia, America, and Europe. These microhaplotypes based on non-binary SNPs have short amplicons, good discrimination power, no stutter artifacts, and have great potential in detection of highly degraded and unbalanced mixtures for personal identification, paternity testing, and ancestry inference.

A highly polymorphic panel of 40-plex microhaplotypes for the Chinese Han population and its application in estimating the number of contributors in DNA mixtures

Microhaplotypes (MHs) have great potential in multiple forensic applications and have proven to be promising markers in complex DNA mixture analysis. In this study, we developed a multiplex panel of 40 highly polymorphic MHs for the Chinese Han population, evaluated its forensic values, and explored its application in predicting the number of contributors (NOCs) in DNA mixtures. The panel consisted of 20 newly proposed loci and 20 previously reported loci with lengths spanning less than 120 bp. The average effective number of alleles (A_e) was 3.77, and the cumulative matching probability (CMP) and the cumulative power of exclusion (CPE) reached 1.2E-37 and 1-2.1E-12, respectively, in the Chinese Han population from the 1000 Genomes Project. Further validation on 150 Chinese Han individuals showed that A_e ranged from 2.62 to 4.41 with a mean value of 3.61, and CMP and CPE were 3.61E-36 and 1-1.84E-12, respectively, indicating that this panel was informative for personal identification and paternity testing in the studied population. To estimate NOC in DNA mixtures, we developed a machine learning model based on this panel. As a result, the accuracies in artificial DNA mixtures reached 95.24% for 2- to 4-person mixtures and 83.33% for 2- to 6-person mixtures. Furthermore, the NOC estimation on simulated profiles with allele dropout showed that this panel was still robust under slight dropout. In conclusion, this panel has value for forensic identification and NOC estimation of DNA mixtures.

Considering the flanking region variants of nonbinary SNP and phenotype-informative SNP to constitute 30 microhaplotype loci for increasing the discriminative ability of forensic applications

The flanking region variants of nonbinary SNPs and phenotype-informative SNPs (piSNPs) have been observed, which may greatly improve the discriminative ability after constituting microhaplotype. In this study, 30 microhaplotype loci based on the nonbinary SNPs and piSNPs (shown to be related to phenotypes such as hair and eye color) were selected. Genotyping were conducted on 100 unrelated northern Han Chinese, and the 26 populations from the 1000 Genome Project were also included for comparison of populations differentiation. The simulated study was conducted for evaluating the efficiency of kinship testing. These 30 microhaplotype loci we selected had good polymorphism, with a mean effective number of alleles (Ae) of 3.46. The average Ae increase was 1.27 compared with the target SNPs. The populations from the five regions worldwide could also be distinguished using these loci. The results of kinship testing showed that these microhaplotype loci had the similar ability as 15 STR loci of AmpFlSTR^R Identifiler^R PCR Amplification Kit to identify the biological parent and a stronger ability to exclude the nonbiological parents. So, these 30 microhaplotype loci may be multifunctional for forensic application, including the ability of personal identification and kinship testing equivalent to 15 STR loci, and the power of ancestry inference for distinguishing the main intercontinental population. Moreover, our selected phenotypic microhaplotype loci may theoretically have phenotype prediction capabilities. But the phenotype prediction efficiency of these phenotypic microhaplotype loci may be worse than that of piSNPs and the detailed prediction accuracy of different populations needs to be further studied.

A Novel SNP-STR System Based on a Capillary Electrophoresis Platform

Various compound markers encompassing two or more variants within a small region can be regarded as generalized microhaplotypes. Many of these markers have been investigated for various forensic purposes, such as individual identification, deconvolution of DNA mixtures, or forensic ancestry inference. SNP-STR is a compound biomarker composed of a single nucleotide polymorphism (SNP) and a closely linked short tandem repeat polymorphism (STR), and possess the advantages of both SNPs and STRs. In addition, in conjunction with a polymerase chain reaction (PCR) technique based on the amplification refractory mutation system (ARMS), SNP-STRs can be used for forensic unbalanced DNA mixture analysis based on capillary electrophoresis (CE), which is the most commonly used platform in worldwide forensic laboratories. Our previous research reported 11 SNP-STRs, but few of them are derived from the commonly used STR loci, for which existing STR databases can be used as a reference. For maximum compatibility with existing DNA databases, in this study, we screened 18 SNP-STR loci, of which 14 were derived from the expanded CODIS core loci set. Stable and sensitive SNP-STR multiplex PCR panels based on the CE platform were established. Assays on simulated two-person DNA mixtures showed that all allele-specific primers could detect minor DNA components in 1:500 mixtures. Population data based on 113 unrelated Chengdu Han individuals were investigated. A Bayesian framework was developed for the likelihood ratio (LR) evaluation of SNP-STR profiling results obtained from two-person mixtures. Furthermore, we report on the first use of SNP-STRs in casework to show the advantages and limitations for use in practice. Compared to 2.86 × 10³ for autosomal STR kits, the combined LR reached 7.14 × 10⁷ using the SNP-STR method in this casework example.

Identification and sequencing of 59 highly polymorphic microhaplotypes for analysis of DNA mixtures

Mixture detection remains one of the major challenges within a forensic science context. In recent years, microhaplotypes were proposed to have great potential in mixture detection, although many of them are not as polymorphic as widely used short tandem repeat (STR) markers. In this study, 59 new highly polymorphic microhaplotypes were identified and sequenced with the NextSeq 500 Sequencer. Based on the whole 1000 Genomes Project dataset, the average effective number of alleles (Ae) of the 59 microhaplotypes was 5.44, and the Ae values of 36 of these microhaplotypes were > 5.00. Their genetic variations in 187 Han Chinese individuals were evaluated. The average allele coverage ratio (ACR) of heterozygotes across all loci was 0.96 ± 0.05. The number of observed alleles varied from 4 to 23, with an average of 8.8 alleles per microhaplotype locus. The average observed heterozygosity (Ho) of 59 loci was 0.77 ± 0.05, and the Ho values of 15 of these loci were > 0.80. All loci showed high polymorphisms with a discrimination power (DP) ranging from 0.80 to 0.97, and the average DP was 0.92 ± 0.03. The analysis of simulated mixtures demonstrated that the microhaplotypes reported here were highly polymorphic and performed well in forensic DNA mixture analysis. This study not only demonstrated the applicability of microhaplotypes in mixture analysis but also provided new choices for highly polymorphic microhaplotypes because after adding the markers identified here, the number of microhaplotypes with Ae values of > 4.00 will increase from ~ 50 to ~ 110.

Evaluation of a Microhaplotype-Based Noninvasive Prenatal Test in Twin Gestations: Determination of Paternity, Zygosity, and Fetal Fraction

As a novel type of genetic marker, the microhaplotype has shown promising potential in forensic research. In the present study, we analyzed maternal plasma cell-free DNA (cfDNA) samples from twin pregnancies to validate microhaplotype-based noninvasive prenatal testing (NIPT) for paternity, zygosity, and fetal fraction (FF). Paternity was determined with the combined use of the relMix package, zygosity was evaluated by examining the presence of informative loci with two fetal genome complements, and FF was assessed through fetal allele ratios. Paternity was determined in 19 twin cases, among which 13 cases were considered dizygotic (DZ) twins based on the presence of 3~10 informative loci and the remaining 6 cases were considered monozygotic (MZ) twins because no informative locus was observed. With the fetal genomic genotypes as a reference, the accuracy of paternity and zygosity determination were confirmed by standard short tandem repeat (STR) analysis. Moreover, the lower FF, higher FF, and combined FF in each DZ plasma sample were closely related to the estimated value. This present preliminary study proposes that microhaplotype-based NIPT is applicable for paternity, zygosity, and FF determination in twin pregnancies, which are expected to be advantageous for both forensic and clinical settings.

A case of heteropaternal superfecundation identified by microhap sequencing of maternal plasma cell-free DNA: A case of HS identified by microhap sequencing

Heteropaternal superfecundation (HS) refers to the fertilization of two or more oocytes by spermatozoa from different male partners during the polyovulatory period. The present study reported a newly discovered case of HS in the 10th week of gestation, in a case of disputed paternity involving a pair of female twins and two alleged fathers (AF₁ and AF₂), based on a custom-designed microhap sequencing assay and R package relMix for data interpretation. The results suggested that the twins had different biological fathers, e.g., HS, and indicated the paternity of AF₁ in relation to one of the twins while excluding AF₂ with regard to both twins. Standard short tandem repeat (STR) analysis was employed to confirm the paternity of the heteropaternal twins. The reported case indicates that HS may occur in paternity cases with dizygotic twins, and microhap, as a novel type of highly polymorphic marker proved to be suitable for mixture deconvolution, should be able to resolve this question effectively and noninvasively at the early stage of pregnancy.

Population genetic data of 74 microhaplotypes in four major U.S. population groups

Microhaplotypes (microhaps or MHs) are novel forensically relevant genetic markers that demand large and appropriate allele frequency datasets for their implementation in casework. In this study we report on the allele frequency data of 74 microhap loci (230 SNPs) included in a newly developed 74-plex assay. The panel was tested on the Ion S5 system on a total of 347 samples from four main U.S. population groups of African, European, East Asian and Southwest Hispanic descent. Overall, frequencies of individual alleles at each locus varied considerably among the different population groups. An increase in the average value of gene diversity was also observed as the number of SNPs per locus increased. Most microhap markers showed no significant deviation from Hardy-Weinberg ratios within any of the individual population samples displaying an average power of discrimination between 0.74 and 0.81 and an average probability of exclusion between 0.32 and 0.39. Moreover, the four population groups had no clear genetic affinities with the exception of U.S. European and U.S. Southwest Hispanic populations, which showed the lowest F_ST value. STRUCTURE and principal component analyses (PCA) analysis resulted in effective clustering of the four populations with the U.S. European and Southwest Hispanic showing some overlap. These results support the potential use of this sequence-based 74plex-microhaplotype assay for ancestry inference in addition to previously reported human identification and mixture deconvolution capabilities.