Mitochondrial DNA typing screens with control region and coding region SNPs

Mitochondrial DNA (mtDNA) analysis has found an important niche in forensic DNA typing. It is used with highly degraded samples or low-copy number materials such as might be found from shed hair or bones exposed to severe environmental conditions. The primary advantage of mtDNA is that it is present in high copy number within cells and therefore more likely to be recovered from highly degraded specimens. A major disadvantage to traditional forensic mtDNA analysis is that it is time-consuming and labor-intensive to generate and review the 610 nucleotides of sequence information commonly targeted in hypervariable regions I and II (HVI and HVII) of the control region. In addition, common haplotypes exist in HVI/HVII mtDNA sequences that can reduce the ability to differentiate two unrelated samples. In this report we describe the utility of two newly available screening assays for rapid exclusion of non-matching samples. The LINEAR ARRAY mtDNA HVI/HVII Region-Sequencing Typing Kit (Roche Applied Science, Indianapolis, IN) was used to type 666 individuals from U.S. Caucasian, African American, and Hispanic groups. Processing of the LINEAR ARRAY probe panels "mito strips" was automated on a ProfiBlot workstation. Observable variation in 666 individuals is reported and frequencies of the mitotypes within and between populations are presented. Samples exhibiting the most common Caucasian mitotype were subdivided with a multiplexed amplification and detection assay using eleven single nucleotide polymorphisms in the mitochondrial genome. These types of screening assays should enable more rapid evaluation of forensic casework samples such that only samples not excluded would be subjected to further characterization through full HVI/HVII mtDNA sequence analysis.     

Optimization of Human mtDNA Control Region Sequencing for Forensic Applications

Sequencing mitochondrial DNA hypervariable regions I and II (HVI and HVII) is useful in forensic missing person and unidentified remains cases. Improvements in ease and sensitivity of testing will yield results from more samples in a timely fashion. Routinely, amplification of HVI and HVII is followed by Sanger sequencing using the BigDye^® Terminator v3.1 Cycle Sequencing kit (Applied Biosystems) using 4 μL of ready reaction mix (RRM). Each sequencing reaction is then purified through column filtration before capillary electrophoresis. Using lower amounts of RRM (2 μL or 1 μL) and purification using BigDye^® XTerminator^? (Applied Biosystems) instead of columns showed no loss of sequence length and increased the quality and the sensitivity of testing, allowing HVI and HVII typing from mitochondrial genome equivalent to 125 fg of nuclear DNA, or 100 pg of HVI/HVII amplicons. Using this methodology, testing can be completed in 1 day, and the cost of testing is reduced.     

Typing the 1.1 kb control region of human mitochondrial DNA in Japanese individuals

This study presents a reliable method that uses high-fidelity long-range PCR and optimized primers to assess polymorphism and to genotype human mitochondrial DNA (mtDNA). This method was used to analyze polymorphic sites in the human mtDNA control region, including hypervariable regions I, II, and III (HVI, HVII, and HVIII), from 124 unrelated Japanese individuals. In HVI, HVII, and HVIII, 80, 37, and 14 polymorphic sites were identified, respectively, excluding those in the homopolymeric cytosine stretch (C-stretch) regions. The region between HVI and HVII also contained 15 polymorphic sites. On the other hand, C-stretch length heteroplasmy in HVI or HVII was observed in 66 of 124 Japanese individuals (53%), which is much higher than in Caucasian populations. The variants in the C-stretch regions were characterized by counting the number of heteroplasmic peaks split from the single peak in homoplasmic sequences (i.e., 16244G and 16255G in HVI and 285G in HVII). Including the C-stretch length heteroplasmy, the 124 Japanese mtDNA samples were classified into 116 distinct haplotypes. The random match probability and the genetic diversity were estimated to be 0.95% and 0.998581, respectively, indicating that the method presented here has higher discrimination than the conventional method for mtDNA typing using HVI and HVII. [Correction added after publication 30 January 2007: in the preceding sentence random match probability and genetic diversity estimates were corrected from 0.95 and 0.998581%, respectively, to 0.95% and 0.998581, respectively.] The haplogroups and their frequencies observed in this study (i.e., D4; 13.7%, M7a1; 11.3%, D4a; 9.7% and M7b2; 8.9%) were similar to those observed in other studies of Japanese mtDNA polymorphism. The method described here is suitable for forensic applications, as shown by successful analysis of tissues from highly putrefied remains of an infant, which allowed maternal relationship to be determined via mtDNA haplotyping.     

High‐Resolution Melting (HRM) of Hypervariable Mitochondrial DNA Regions for Forensic Science

Forensic strategies commonly are proceeding by analysis of short tandem repeats (STRs); however, new additional strategies have been proposed for forensic science. Thus, this article standardized the high‐resolution melting (HRM) of DNA for forensic analyzes. For HRM, mitochondrial DNA (mtDNA) from eight individuals were extracted from mucosa swabs by DNAzol reagent, samples were amplified by PCR and submitted to HRM analysis to identify differences in hypervariable (HV) regions I and II. To confirm HRM, all PCR products were DNA sequencing. The data suggest that is possible discriminate DNA from different samples by HRM curves. Also, uncommon dual‐dissociation was identified in a single PCR product, increasing HRM analyzes by evaluation of melting peaks. Thus, HRM is accurate and useful to screening small differences in HVI and HVII regions from mtDNA and increase the efficiency of laboratory routines based on forensic genetics.     

Optimization of a duplex amplification and sequencing strategy for the HVI/HVII regions of human mitochondrial DNA for forensic casework

A duplex primer set for the amplification of mitochondrial DNA HVI and HVII control regions was evaluated for the optimization of a DNA sequencing protocol suitable for forensic casework. HVI and HVII products, with the absence of non-specific products, could be detected by agarose gel electrophoresis when as little as 0.5 and 0.1pg of DNA were amplified for 34 and 38 cycles, respectively. Because HVI and HVII amplicons are co-synthesized in the duplex PCR, fewer steps are required (lessening the risk of cross contamination events) and more frugal use of precious extracted DNA samples is possible, both desirable features for forensic casework. The ABI Prism BigDyetrade mark version 1.1 chemistry provided high quality sequencing data, with little or no background noise and uniform peak heights, outcomes that favored reliable detection of heteroplasmy, particularly at early sequence reads (<40 bases). Optimal compromise between sensitivity and sequence accuracy in the absence of noise was achieved starting at 150 mitochondrial genome copies. The protocol is effective (no sequence errors) with highly degraded DNA (average detectable template size of 200bp). Dual artificial template mixtures with the minor component at 15% suggests that heteroplasmy should be detected at this level with confidence.     

MtSNP typing before mtDNA sequencing: Why do it?

Analysis of control mitochondrial DNA (mtDNA) hypervariable regions is sometimes the only available method to study hair evidence in forensic casework although being a laborious technique. Nowadays there is a huge interest in new genetic markers such as single nucleotide polymorphisms (SNPs) to type degraded forensic samples. For that purpose, a 10-Plex mitochondrial SNP for haplogroup typing, chosen from several SNP studies and useful to study the most common populations in our laboratory was applied in forensic casework. Hair shafts from three forensic cases with different ethnic backgrounds were studied with mtDNA sequencing and compared with mitochondrial SNPs (mtSNPs) study. Coding mtSNP typing prior to sequencing can allow for a rapid screening in forensic casework, which is emphasized in the first two cases. Moreover, in cases in which mtDNA sequencing fails, mtSNPs can still be detected. This 10 SNP loci multiplex provides a less expensive and simpler method for mitochondrial typing compared to control region mtDNA sequencing, especially when used as a fast screening method.     

Different informativeness of the three hypervariable mitochondrial DNA regions in the population of Bologna (Italy)

Mitochondrial DNA (mtDNA) sequence variations at hypervariable regions HVI, HVII and HVIII were analysed in 100 unrelated Italians from Bologna. The values of the statistical parameters are in agreement with the range of European populations. We suggest that the less informative HVIII region may be useful to distinguish HVI-HVII identical sequences in forensic analysis especially when nuclear DNA cannot be investigated.     

粪便DNA提取及检验

目的　研究人类粪便DNA的提取和检验方法。方法　 8人份粪便样本 ,磁珠法提取DNA后 ,进行STR复合扩增和mtDNAHVI区测序分析。结果　用 2种方法提取的粪便DNA ,STR复合扩增检验均未获成功 ;方法1提取的粪便DNA有 6个样本、方法 2有 7个样本获得了清晰可读的mtDNAHVI区序列 ,并与唾液对照样本DNA的序列完全一致。结论　用本文建立的方法提取粪便DNA ,不适于STR分析 ,可通过mtDNA测序分析进行检验。     

The Use of Mitochondrial DNA Single Nucleotide Polymorphisms to Assist in the Resolution of Three Challenging Forensic Cases

Abstract:  Mitochondrial DNA (mtDNA) single nucleotide polymorphisms (SNPs) in an 11-plex assay were typed in three missing person cases involving highly degraded human remains. Unlike the traditional forensic approach to analyzing mtDNA which focuses on sequencing portions of the noncoding Control Region, this assay targets discriminatory SNPs that reside principally in the coding region. In two of the cases, the SNP typing successfully excluded one of two reference families that could not be excluded on the basis of mtDNA hypervariable region sequencing alone, and resulted in the final resolution of both decades-old cases. In a third case, SNP typing confirmed the sorting and reassociation of multiple commingled skeletal elements. The application of a specific mtDNA SNP assay in these cases demonstrates its utility in distinguishing samples when the most common Caucasian hypervariable region type is encountered in forensic casework.     

SSCP法mtDNA分型的法医学应用

目的探讨SSCP法mtDNA分型在法医鉴定实践中的意义。方法PCR扩增mtDNAHV-I和HV-II的序列多态性片段,直接用SSCP技术分型。对70个湖北汉族真三联家系和140例随机个体进行检测,比较家系中mtDNA的单倍型SSCP图谱。统计分析SSCP法用于两个高变区在母系确定、个人识别中的意义和鉴别能力。结果在70个家系中,母亲和孩子的HV-I、HV-IISSCP带型完全相同;家系中父亲与母子的HV-I图谱不同占98.57%;HV-IISSCP图谱不同占97.13%。140例随机个体的HVI、HVII区分别检出21、16种单倍型,GD值分别为0.9556、0.9356。结论mtDNA-SSCP分型在嫌疑人筛查和母系亲缘关系推断中有实际应用价值。     

A rape case solved by mitochondrial DNA mixture analysis

In cases of stains that contain mixed DNA from different contributors, analyzing mitochondrial DNA (mtDNA) requires the use of cloning techniques. We developed an efficient cloning technique that was applied in a rape case. After a differential lysis-based DNA extraction from vaginal swabs, hypervariable region I and II (HVI, HVII) amplicons obtained from the male fraction were cloned. Although we mainly found the victim's haplotype, we were able to detect the suspect's haplotype in two clones for HVI and in one clone for HVII. As the midpiece of the flagellum, which contains mitochondria, can be lost during the differential lysis, we also investigated the female fraction by cloning to evaluate the proportion of victim/suspect mtDNA. Unfortunately, only clones presenting the victim's haplotype were found. This case highlights the need for an optimal differential lysis protocol to enrich the male fraction not only with nuclear but also mitochondrial DNA.     

Detection of sequence variation in the HVII region of the human mitochondrial genome in 689 individuals using immobilized sequence-specific oligonucleotide probes

We have developed a rapid, immobilized probe-based assay for the detection of sequence variation in the hypervariable segment II (HVII) of the mitochondrial DNA (mtDNA) control region. Using a panel of 17 sequence-specific oligonucleotide (SSO) probes immobilized on nylon membrane strips, we typed 689 individuals from four population groups. The genetic diversity value for each population was calculated from the frequency data, and the frequencies of distinct "mitotypes" in each group were determined. We performed DNA sequence analysis of 129 samples to characterize the sequences associated with "blanks" (absence of probe signals) and weak probe signals. Out of 689 samples, we observed five heteroplasmic samples (excluding the variable C-stretch beginning at position 303) using the immobilized SSO probe panel. The SSO probe strips were used for the analysis of shed hairs and bloodstains from several criminal cases in Sweden, one of which is described here. We conclude that this mtDNA typing system is useful for human identification and significantly decreases casework turnaround time.     

Is it possible to differentiate mtDNA by means of HVIII in samples that cannot be distinguished by sequencing the HVI and HVII regions?

The mitochondrial control region includes three so-called hypervariable (HV) regions, in which the polymorphic positions show a particularly high frequency. According to a population study of 200 unrelated individuals from Germany, HVI (positions 16,024-16,365, according to Anderson) showed 88 variable positions in a total length of 342 bp (26%) and HVII (positions 73-340) displayed 65 mutable sites in 268 bp (24%). HVIII (positions 438-574) exhibited a slightly lower variability, with 25 polymorphic sites within 137 bp (18%), but contrasted clearly with the background, which showed variability rates of only 7% (positions 16,366-16,569, 1-72) and 3% (positions 341-437), respectively. At present, the displacement (D)-loop database in Magdeburg comprises 904 sequences of the mitochondrial HVI region and HVII region from Germans, Austrians and Swiss. By means of this material, the extent to which the mtDNA sequences that do not differ in the HVI and HVII regions can be differentiated by additionally sequencing HVIII was investigated.     

Results of a collaborative study of the EDNAP group regarding mitochondrial DNA heteroplasmy and segregation in hair shafts

A collaborative exercise was carried out by the European DNA Profiling Group (EDNAP) in order to evaluate the distribution of mitochondrial DNA (mtDNA) heteroplasmy amongst the hairs of an individual who displays point heteroplasmy in blood and buccal cells. A second aim of the exercise was to study reproducibility of mtDNA sequencing of hairs between laboratories using differing chemistries, further to the first mtDNA reproducibility study carried out by the EDNAP group. Laboratories were asked to type 2 sections from each of 10 hairs, such that each hair was typed by at least two laboratories. Ten laboratories participated in the study, and a total of 55 hairs were typed. The results showed that the C/T point heteroplasmy observed in blood and buccal cells at position 16234 segregated differentially between hairs, such that some hairs showed only C, others only T and the remainder, C/T heteroplasmy at varying ratios. Additionally, differential segregation of heteroplasmic variants was confirmed in independent extracts at positions 16093 and the poly(C) tract at 302-309, whilst a complete A-G transition was confirmed at position 16129 in one hair. Heteroplasmy was observed at position 16195 on both strands of a single extract from one hair segment, but was not observed in the extracts from any other segment of the same hair. Similarly, heteroplasmy at position 16304 was observed on both strands of a single extract from one hair. Additional variants at positions 73, 249 and the HVII poly(C) region were reported by one laboratory; as these were not confirmed in independent extracts, the possibility of contamination cannot be excluded. Additionally, the electrophoresis and detection equipment used by this laboratory was different to those of the other laboratories, and the discrepancies at position 249 and the HVII poly(C) region appear to be due to reading errors that may be associated with this technology. The results, and their implications for forensic mtDNA typing, are discussed in the light of the biology of hair formation.     

Variability of the Entire Mitochondrial DNA Control Region in a Human Isolate from the Pas Valley (Northern Spain)

Abstract: In this study, we analyzed the entire mtDNA control region in 61 unrelated individuals from the Pas Valley (Cantabria), a human isolate from northern Spain, to evaluate the suitability of this analysis to increase the power of discrimination of this locus for forensic purposes in human isolates. Low values obtained for the diversity parameters confirmed the relative isolation of this human group. The main findings of this study indicated that even the analysis of the entire mtDNA control region may have important limitations for use in forensic casework when dealing with human isolates: none of the 44 individuals who exhibited identical HVI‐HVII haplotypes could be further differentiated by analysis of segment HVIII. Nevertheless, analysis of the entire mtDNA control region proved to be useful to determine the ancestry of the samples examined, by contributing to the confirmation, and, on occasion, even to the refinement of the haplogroup assignment.     

The EDNAP mitochondrial DNA population database (EMPOP) collaborative exercises: organisation, results and perspectives

This paper presents an overview of the organisation and the results of the collaborative exercises (CE) of the European DNA Profiling (EDNAP) Group's mitochondrial DNA population database project (EMPOP). The aim of the collaborative exercises was to determine whether uniformity of mtDNA sequencing results could be achieved among different laboratories. These were asked to sequence either the complete mtDNA control region or the two hypervariable regions HVI (16024-16365) and HVII (73-340) from DNA extracts, buccal swabs or bloodstains, proceeding in accordance with the protocol and strategies used in each individual laboratory. The results of the collaborative exercises were employed to identify possible sources of errors that could arise during the analysis and interpretation of mtDNA profiles. These findings were taken as a basis to tentatively make suitable arrangements for the construction of a high quality mtDNA database. One hundred fifty mtDNA profiles were submitted to the evaluating laboratory, and disaccording profiles were classified into four groups corresponding to the source of error: clerical errors, sample mix-ups, contaminations and discrepancies with respect to the mtDNA nomenclature. Overall, 14 disaccording haplotypes (16 individual errors) were observed. The errors included 10 clerical errors, 3 interpretation problems, 2 cases of sample mix-up and 1 case of point heteroplasmic mixture, where the 2 sequencing reactions brought inconsistent base calls. This corresponds to an error rate of 10.7% in a virtual mtDNA database consisting of the collaborative exercise results. However, this estimate is still conservative compared to conclusions drawn by authors of meanwhile numerous publications critically reviewing published mtDNA population databases. Our results and earlier published concerns strongly emphasize the need for appropriate safety regulations when mtDNA profiles are compiled for database purposes in order to accomplish the high standard required for mtDNA databases that are used in the forensic context.     

Analysis of eight mtDNA coding region polymorphisms for characterization of the female lineages ancestry in Alagoas,Brazil

In this work we evaluated eight mitochondrial DNA coding region polymorphisms (8281–8289d, 1736, 13263, 4883, 3594, 10873, 10400, and 12705) in order to identify lineages of African, Amerindian and European origin in Alagoas, Northeastern Brazil. Seven of these polymorphisms were detected by multiplex minisequencing with SnaPshot. For validation purposes a sample previously characterized by sequencing of the HVI and HVII regions was analyzed. Good agreement was observed between the phylogenetic results obtained in this work and the HVI and HVII regions sequencing. The results obtained suggest that the set of markers evaluated in this study can be used in ancestry studies of Brazilian populations.     

Detection and quantification of the age-related point mutation A189G in the human mitochondrial DNA

Mutation analysis in the mitochondrial DNA (mtDNA) control region is widely used in population genetic studies as well as in forensic medicine. Among the difficulties linked to the mtDNA analysis, one can find the detection of heteroplasmy, which can be inherited or somatic. Recently, age-related point mutation A189G was described in mtDNA and shown to accumulate with age in muscles. We carried out the detection of this 189 heteroplasmic point mutation using three technologies: automated DNA sequencing, Southern blot hybridization using a digoxigenin-labeled oligonucleotide probe, and peptide nucleic acid (PNA)/real-time PCR combined method on different biological samples. Our results give additional information on the increase in mutation frequency with age in muscle tissue and revealed that the PNA/real-time PCR is a largely more sensitive method than DNA sequencing for heteroplasmy detection. These investigations could be of interest in the detection and interpretation of mtDNA heteroplasmy in anthropological and forensic studies.     

A DNA microarray system for forensic SNP analysis

Forensic DNA analysis is routinely performed using polymorphic short tandem repeat (STR) markers. However, for degraded or minute DNA samples, analysis of autosomal single nucleotide polymorphisms (SNPs) in short fragments might be more successful. Furthermore, sequencing of mitochondrial DNA (mtDNA) is often performed on highly degraded or scarce samples due to the high copy number of mtDNA in each cell. Due to the increasing number of complete mtDNA genome sequences available, the limited discrimination power of an mtDNA analysis, may be increased by analysis of coding region polymorphisms in addition to the non-coding variation. Since sequence analysis of the coding region would require more material than generally present in forensic samples, an alternative SNP analysis approach is required. We have developed a one-colour microarray-based SNP detection system for limited forensic materials. The method is based on minisequencing in solution prior to hybridisation to universal tag-arrays. In a first outline of a forensic chip, a combination of 12 nuclear and 21 mitochondrial SNP markers are analysed simultaneously. The mitochondrial markers on the chip are polymorphisms within the hypervariable region as well as in the coding region. Even though the number of markers in the current system is limited, it can easily be extended to yield a greater power of discrimination. When fully developed, microarray analysis provides a promising system for efficient sensitive SNP analysis of forensic samples in the future.     

Typing of mitochondrial DNA coding region SNPs of forensic and anthropological interest using SNaPshot minisequencing

The development of new methodologies for high-throughput SNP analysis is one of the most stimulating areas in genetic research. Here, we describe a rapid and robust assay to simultaneously genotype 17 mitochondrial DNA (mtDNA) coding region SNPs by minisequencing using SNaPshot. SNaPshot is a methodology based on a single base extension of an unlabeled oligonucleotide with labeled dideoxy terminators. The set of SNPs implemented in this multiplexed SNaPshot reaction allow us to allocate common mitochondrial West Eurasian haplotypes into their corresponding branch in the mtDNA skeleton, with special focus on those haplogroups lacking unambiguous diagnostic positions in the first and second hypervariable regions (HVS-I/II; by far, the most common segments analyzed by sequencing). Particularly interesting is the set of SNPs that subdivide haplogroup H; the most frequent haplogroup in Europe (40–50%) and one of the most poorly characterized phylogenetically in the HVS-I/II region. In addition, the polymorphic positions selected for this multiplex reaction increase considerably the discrimination power of current mitochondrial analysis in the forensic field and can also be used as a rapid screening tool prior to full sequencing analysis. The method has been validated in a sample of 266 individuals and shows high accuracy and robustness avoiding both the use of alternative time-consuming classical strategies (i.e. RFLP typing) and the need for high quantities of DNA template.