Sohee Cho

Multiple Polymorphic Loci for Molecular Typing of Strains of Mycobacterium leprae

ABSTRACT The need for molecular tools for the differentiation of isolates of Mycobacterium leprae, the organism that causes leprosy, is urgent in view of the continuing high levels of new case detection, despite years of aggressive chemotherapy and the consequent reduction in the prevalence of leprosy. The slow onset of leprosy and the reliance on physical examination for detection of disease have restricted the epidemiological tracking necessary to understand and control transmission. Two genetic loci in several isolates of M. leprae have previously been demonstrated to contain variable-number tandem repeats (VNTRs). On the basis of these reports and the availability of the full genome sequence, multiple-locus VNTR analysis for strain typing has been undertaken. A panel of 11 short tandem repeat (STR) loci with repeat units of 1, 2, 3, 6, 12, 18, 21, and 27 bp from four clinical isolates of M. leprae propagated in armadillo hosts were screened by PCR. Fragment length polymorphisms were detected at 9 of the 11 loci by agarose gel electrophoresis. Sequencing of representative DNA products confirmed the presence of VNTRs between isolates. The application of nine new polymorphic STRs in conjunction with automated methods for electrophoresis and size determination allows greater discrimination between isolates of M. leprae and enhances the potential of this technique to track the transmission of leprosy.

Independent validation of DNA-based approaches for age prediction in blood

Numerous molecular biomarkers have been proposed as predictors of chronological age. Among them, T-cell specific DNA rearrangement and DNA methylation markers have been introduced as forensic age predictors in blood because of their high prediction accuracy. These markers appear highly promising, but for better application to forensic casework sample analysis the proposed markers and genotyping methods must be tested further. In the current study, signal-joint T-cell receptor excision circles (sjTRECs) and DNA methylation markers located in the ELOVL2, C1orf132, TRIM59, KLF14, and FHL2 genes were reanalyzed in 100 Korean blood samples to test their associations with chronological age, using the same analysis platform used in previous reports. Our study replicated the age association test for sjTREC and DNA methylation markers in the 5 genes in an independent validation set of 100 Koreans, and proved that the age predictive performance of the previous models is relatively consistent across different population groups. However, the extent of age association at certain CpG loci was not identical in the Korean and Polish populations; therefore, several age predictive models were retrained with the data obtained here. All of the 3 models retrained with DNA methylation and/or sjTREC data have a CpG site each from the ELOVL2 and FHL2 genes in common, and produced better prediction accuracy than previously reported models. This is attributable to the fact that the retrained model better fits the existing data and that the calculated prediction accuracy could be higher when the training data and the test data are the same. However, it is notable that the combination of different types of markers, i.e., sjTREC and DNA methylation, improved prediction accuracy in the eldest group. Our study demonstrates the usefulness of the proposed markers and the genotyping method in an independent dataset, and suggests the possibility of combining different types of DNA markers to improve prediction accuracy.

Age estimation via quantification of signal-joint T cell receptor excision circles in Koreans

The estimation of age from biological samples (i.e., remains) at crime scenes could provide useful information about both victims and other persons related to criminal activities. Signal-joint T cell receptor excision circle (sjTREC) levels in peripheral blood decline with age, and negative correlations between sjTREC levels and age have been demonstrated in several ethnic groups. To validate the utility of sjTREC for age estimation in Koreans, Taqman qPCR was used to quantify the sjTREC level in samples obtained from 172 individuals ranging from 16 to 65 years old. We modified the previously reported method by using a shorter amplicon and confirmed the efficiency and utility of this method in this report. Our results showed that the linear negative regression curve between sjTREC levels and age was characterized by r=-0.807 and a standard error of 8.49 years. These results indicate that sjTREC level is an effective age estimation method in Koreans. The value of the standard error of quantification was not different from previous reports for other population groups.

Forensic application of SNP-based resequencing array for individual identification

In forensic field investigations using single nucleotide polymorphism (SNP) have been performed for various purposes. Based on the characteristics of SNP, it is essential to have a multi-amplification technology and a platform to analyze the amplified SNP markers accurately. Here, we have developed a platform based on the resequencing array of Affymetrix analyzing 169 SNP markers amplified via multiplex PCR and verified its forensic application. From the 1000 genomes database, the SNP markers were selected under the condition of less than 0.04 fixation index (Fst) and 0.3 linkage disequilibrium (LD) R(2) value, and 0.4-0.5 minor allele frequency (MAF). It was identified that more than 120 out of 169 SNPs were able to be typed with approximately 10pg of DNA and artificially degraded samples in various tests. The DNA extracted from bones also showed a similar rate of success. The results indicated that our platform has a potential role to assist the current short tandem repeat (STR) method in analyzing harsh samples, such as bone or degraded DNA. With a possibility to expand the platform, it was expected to apply to various uses in different areas in the future.

Entire Mitochondrial DNA Sequencing on Massively Parallel Sequencing for the Korean Population

Mitochondrial DNA (mtDNA) genome analysis has been a potent tool in forensic practice as well as in the understanding of human phylogeny in the maternal lineage. The traditional mtDNA analysis is focused on the control region, but the introduction of massive parallel sequencing (MPS) has made the typing of the entire mtDNA genome (mtGenome) more accessible for routine analysis. The complete mtDNA information can provide large amounts of novel genetic data for diverse populations as well as improved discrimination power for identification. The genetic diversity of the mtDNA sequence in different ethnic populations has been revealed through MPS analysis, but the Korean population not only has limited MPS data for the entire mtGenome, the existing data is mainly focused on the control region. In this study, the complete mtGenome data for 186 Koreans, obtained using Ion Torrent Personal Genome Machine (PGM) technology and retrieved from rather common mtDNA haplogroups based on the control region sequence, are described. The results showed that 24 haplogroups, determined with hypervariable regions only, branched into 47 subhaplogroups, and point heteroplasmy was more frequent in the coding regions. In addition, sequence variations in the coding regions observed in this study were compared with those presented in other reports on different populations, and there were similar features observed in the sequence variants for the predominant haplogroups among East Asian populations, such as Haplogroup D and macrohaplogroups M9, G, and D. This study is expected to be the trigger for the development of Korean specific mtGenome data followed by numerous future studies.

Assessment of mitochondrial DNA heteroplasmy detected on commercial panel using MPS system with artificial mixture samples

Mitochondrial DNA (mtDNA) heteroplasmy is a potential genetic marker for forensic mtDNA analysis as well as phylogenic studies. Frequency of mtDNA heteroplasmy has been investigated in different populations through massively parallel sequencing (MPS) analysis, revealing various levels of frequency based on different MPS systems. For accurate heteroplasmy identification, it is essential to explore reliable detection threshold on various MPS systems. In addition, software solutions and pipelines need to be evaluated to analyze data effectively. In this study, heteroplasmy analysis was conducted on a commercially available mtDNA analysis system developed for forensic caseworks with artificially mixed DNA samples known for ratios and variant positions for assessment. mtDNA heteroplasmy > 10% was detectable with Torrent Variant Caller (TVC) while lower levels were identified using GeneMarker® HTS specialized software for minor variant detection. This study implies that analytical parameters and tools need to be optimized and evaluated for low-level heteroplasmy identification. Automated system with simple and efficient workflow is needed for forensic caseworks.

Differences of PCR efficiency between two-step PCR and standard three-step PCR protocols in short tandem repeat amplification

The effects on STR typing results, using a two-step PCR protocol that combines the annealing and extension steps, were determined using samples at various DNA concentrations. DNA samples ranging from 62.5 to 500 pg were amplified using the reagents contained within the AmpFlSTR Identifiler PCR Amplification Kit. At 250–500 pg of DNA template, the rates of detecting alleles were close to those found when using three-step PCR (the standard Identifiler protocol) and two-step PCR protocols. The two-step PCR increased by 8.1% and 64.2% the average number of amplified alleles compared with the three-step PCR at 125 pg and 62.5 pg of template DNA, respectively. At 62.5–500 pg of DNA, the average peak heights were 23.3–65.0% higher than heights using the three-step PCR protocol. When two different PCR protocols were applied to old bones, the average number of amplified loci was similar. These results suggested that the two-step PCR protocol can generate more STR alleles in low template DNA samples; however, the method may be limited with samples of very low-quality, i.e., degraded DNA, compared with the three-step protocol. A better understanding of the effects of the two-step PCR protocol on amplification conditions might help researchers improve STR typing.

Kinship Testing Based on SNPs Using Microarray System

Background: Kinship testing using biallelic SNP markers has been demonstrated to be a promising approach as a supplement to standard STR typing, and several systems, such as pyrosequencing and microarray, have been introduced and utilized in real forensic cases. The Affymetrix microarray containing 169 autosomal SNPs developed for forensic application was applied to our practical case for kinship analysis that had remained inconclusive due to partial STR profiles of degraded DNA and possibility of inbreeding within the population. Case Report: 169 autosomal SNPs were typed on array with severely degraded DNA of two bone samples, and the kinship compared to genotypes in a reference database of their putative family members. Results: Two bone samples remained unidentified through traditional STR typing with partial profiles of 10 or 14 of 16 alleles. Because these samples originated from a geographically isolated population, a cautious approach was required when analyzing and declaring true paternity only based on PI values. In a supplementary SNP typing, 106 and 78 SNPs were obtained, and the match candidates were found in each case with improved PI values than using only STRs and with no discrepant SNPs in comparison. Conclusion: Our case showed that the utility of multiple SNPs on array is expected in practical forensic caseworks with an establishment of reference database.

Genetic resolution of applied biosystems™ precision ID Ancestry panel for seven Asian populations

Massively parallel sequencing (MPS) offers additional information in cases that lack reference samples for comparison. The HID-Ion AmpliSeq Ancestry Panel is a forensic multiplex platform consisting of 165 autosomal markers designed to provide biogeographic ancestry information. We analyzed seven different population groups from Asia to assess the accuracy and reliability of analysis, using this panel. In this study, we have designated 750 unrelated Asians, from southern China (n = 99), Beijing (n = 100), Japan (n = 101), Korea (n = 100), Vietnam (n = 100), Nepal (n = 100), India (n = 51), and Pakistan (n = 99). The likelihood ratios of 750 Asians were calculated, using the Torrent Server and the HID SNP Genotyper Plugin Version 4.3.2. The results reveal that all Northeast Asians (China, Japan, and Korea), and Vietnamese, were predicted as East Asians with the highest ethnicity likelihood values from reference data. Although the samples from Nepal, India and Pakistan (Southwest Asians), were predominantly predicted as South Asians, there were seven cases of which results revealed as Europeans, with similar likelihood patterns. Population structure analysis indicated that Southwest Asians have a genetic profile that is distinguishable from those of other Asian populations. This panel was validated for potential usefulness in forensic analysis and the findings could be used as a basis for building additional Asian specific reference databases. Nevertheless, additional analyses comprising larger sample sizes will be necessary, especially Southeast Asians, to fully understand the Asian population structure, and to discriminate them with further details.

Set up of cutoff thresholds for kinship determination using SNP loci

The usefulness of single nucleotide polymorphism (SNP) loci for kinship testing has been demonstrated in many case works, and suggested as a promising marker for relationship identification. For interpreting results based on the calculation of the likelihood ratio (LR) in kinship testing, it is important to prepare cutoffs for respective relatives which are dependent on genetic relatedness. For this, analysis using true pedigree data is significant and reliable as it reflects the actual frequencies of markers in the population. In this study, the kinship index was explored through 1209 parent-child pairs, 1373 full sibling pairs, and 247 uncle-nephew pairs using 136 SNP loci. The cutoffs for LR were set up using different numbers of SNP loci with accuracy, sensitivity, and specificity. It is expected that this study can support the application of SNP loci-based kinship testing for various relationships.