Validation of a 17-locus Y-STR multiplex system

Internal validation of a commercial 17-locus Y-STR system (AmpFlSTR^® Yfiler™, Applied Biosystems) has been performed on the ABI PRISM^® 3130 Genetic Analyzer for use in forensic cases. The Yfiler™ kit was validated according to SWGDAM guidelines. Our results show that it is possible to obtain full profiles with as little as 30 pg of male DNA even in the presence of 20,000-fold amounts of female DNA. Reaction volume was optimized for 10 μl. Male-male mixtures yielded full profiles of the minor contributor with 10-fold excess of the major contributor. Stutter values for each locus were determined from data generated for the population study which included Y-STR profiles from 156 caucasian males from the Montreal and Lac St.-Jean areas of Québec, Canada. The study recorded 141 different haplotypes of which 131 were unique with a haplotype diversity of 0.9965. A number of non-probative forensic samples from rape kit epithelial fractions and fingernail scrapings were also successfully tested.     

SWGDAM developmental validation of a 19-locus Y-STR system for forensic casework

A Scientific Working Group on DNA Analysis Methods (SWGDAM) developmental validation study was carried out on two Y-STR multiplex systems (MPI and MPII) that collectively permit the co-amplification of 19 Y-STR markers, including DYS393, DYS392, DYS391, DYS389I, DYS389II, Y-GATA-A7.2 (DYS461), DYS438, DYS385a and DYS385b (MPI); DYS425, DYS388, DYS390, DYS439, DYS434, DYS437, Y-GATA-C.4, Y-GATA-A7.1 (DYS460), Y-GATA-H.4, and DYS 19 (MPII). Performance checks subsequent to PCR parameter optimization indicated that MPI and MPII were suitably reproducible, precise and accurate for forensic use. The sensitivity of the systems was such that a full 19-locus Y-STR profile was obtainable with 150-200 pg of male DNA, and some loci were detectable even with as little as 20-30 pg of input DNA. Primate specificity was demonstrated by the lack of cross-reactivity with a variety of commonly encountered bacterial and animal species, with the single exception of a monomorphic canine product that was outside of the size range of human alleles from any of the 19 loci. Not surprisingly, cross-reactivity was observed with a number of male and female nonhuman primates. Environmentally compromised samples produced full or partial Y-STR profiles. For example, a semen stain exposed to the outdoor elements for six months still gave a 13-locus Y-STR profile. Although a limited number of female DNA artifacts were observed in mixed stains in which the male DNA comprised 1/300 of the total, the full 19-locus male profile was easily discernible. Even at a 1500-to-2000-fold dilution of male DNA with female DNA partial Y-STR profiles were obtained. Furthermore, the potential utility of MPI and MPII for forensic casework is exemplified by their ability to dissect out the male haplotype in a variety of case-type samples, including, inter alia, post-coital vaginal swabs, admixed male and female bloodstains, the nonsperm fraction from a differentially extracted semen stain, and determination of the number of male donors in mixed semen stains.     

MiniFiler试剂盒运用于法医微量物证的检验

目的应用MiniFiler试剂盒对法医微量物证进行DNA分析。方法采用MiniFiler试剂盒对样本进行DNA分型,确定样本9个STR基因座的等位基因型。结果10pg DNA模板经MiniFiler试剂盒扩增后,能够进行DNA分型,但40pg以上的DNA方可得到稳定可靠的分型结果。结论MiniFiler试剂盒可以用于法医微量物证的STR分析。     

Evaluation of Degradation in DNA from Males with a Quantitative Gender Typing,Endpoint PCR Multiplex

Evidentiary samples submitted to a forensic DNA laboratory occasionally yield DNA that is degraded. Samples of intact chromosomal DNA (both nuclear and mitochondrial) were subjected to a heating protocol to induce DNA degradation. The DNAs were then analyzed using a multiplex PCR assay that amplifies targets of low and high molecular weight on the X/Y and mitochondrial chromosomes. If degradation is random, the amplification of larger DNA targets should be more adversely affected by degradation than smaller targets. In nuclear and mitochondrial DNA from a male donor, exhibiting degradation, DNA quantity estimates based upon higher molecular weight amplicons (HMW) are significantly lower than estimates made using low molecular weight (LMW) Q‐TAT amplicons. DNA degradation estimated using this approach correlated well with actual fluorescence associated with HMW and LMW STR alleles amplified from the same genomic DNA templates. Q‐TAT is thus useful not only as a quantitation tool, but also as an indicator of template degradation.     

AGCU Mini系统在法医学中的应用

目的考察及评价AGCU Mini系统在法医学实践中的应用价值。方法应用AGCU Mini系统检测12 775份陈旧血样,进行梯度DNA模板浓度分析,并与IdentifilerTM试剂盒检测结果进行比对,评价体系的检测成功率及方法的灵敏度。针对AGCU Mini系统中D19S253基因座,对699份浙江汉族无关个体进行多态性调查。结果 12 775份陈旧血样采用AGCU Mini试剂盒检测,12 885份(96.1%)分型成功,检测灵敏度为40pg(10μL体系),方法成功率及灵敏度均高于IdentifilerTM试剂盒。D19S253基因座共检出9个等位基因,频率范围为0.005 7～0.316 2,杂合度为0.814 0,多态性信息含量为0.772 9。结论 AGCU Mini系统可用于法医微量物证的STR分析,与相关试剂盒联合使用价值更高。     

LoComatioN: a software tool for the analysis of low copy number DNA profiles

Previously, the interpretation of low copy number (LCN) STR profiles has been carried out using the biological or 'consensus' method-essentially, alleles are not reported, unless duplicated in separate PCR analyses [P. Gill, J. Whitaker, C. Flaxman, N. Brown, J. Buckleton, An investigation of the rigor of interpretation rules for STRs derived from less than 100 pg of DNA, Forens. Sci. Int. 112 (2000) 17-40]. The method is now widely used throughout Europe. Although a probabilistic theory was simultaneously introduced, its time-consuming complexity meant that it could not be easily applied in practice. The 'consensus' method is not as efficient as the probabilistic approach, as the former wastes information in DNA profiles. However, the theory was subsequently extended to allow for DNA mixtures and population substructure in a programmed solution by Curran et al. [J.M. Curran, P. Gill, M.R. Bill, Interpretation of repeat measurement DNA evidence allowing for multiple contributors and population substructure, Forens. Sci. Int. 148 (2005) 47-53]. In this paper, we describe an expert interpretation system (LoComatioN) which removes this computational burden, and enables application of the full probabilistic method. This is the first expert system that can be used to rapidly evaluate numerous alternative explanations in a likelihood ratio approach, greatly facilitating court evaluation of the evidence. This would not be possible with manual calculation. Finally, the Gill et al. and Curran et al. papers both rely on the ability of the user to specify two quantities: the probability of allelic drop-out, and the probability of allelic contamination ("drop-in"). In this paper, we offer some guidelines on how these quantities may be specified.     

The Potential of Cosmetic Applicators as a Source of DNA for Forensic Analysis

Personal products, such as toothbrushes, have been used as both known reference and evidentiary samples for forensic DNA analysis. This study examined the viability of a broad selection of cosmetic applicators for use as targets for human DNA extraction and short tandem repeat (STR) analysis using standard polymerase chain reaction (PCR) conditions. Applicator types included eyeliner smudgers, pencils and crayons, eye shadow sponges, mascara wands, concealer wands, face makeup sponges, pads and brushes, lipsticks and balms, and lip gloss wands. The quantity and quality of DNA extracted from each type of applicator were examined by assessing the number of loci successfully amplified and the peak balance of the heterozygous alleles in each full STR profile. While degraded DNA, stochastic amplification, and PCR inhibition were observed for some items, full STR profiles were developed for 14 of 76 applicators. The face makeup sponge applicators yielded the highest proportional number of full STR profiles (4/7).     

Validation of male-specific, 12-locus fluorescent short tandem repeat (STR) multiplex

Y chromosome-specific short tandem repeat (Y-STR) analysis has become another widely accepted tool for human identification. The PowerPlex Y System is a fluorescent multiplex that includes the 12 loci: DYS19, DYS385a/b, DYS389I/II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438 and DYS439. This panel of markers incorporates the 9-locus European minimal haplotype (EMH) loci recommended by the International Y-STR User Group and the 11-locus set recommended by the Scientific Working Group on DNA Analysis Methods (SWGDAM). Described here are inter-laboratory results from 17 developmental validation studies of the PowerPlex Y System and include the following results: (a) samples distributed between laboratories and commercial standards produced expected and reproducible haplotypes; (b) use of common amplification and detection instruments were successfully demonstrated; (c) full profiles were obtained with standard 30 and 32 cycle amplification protocols and cycle number (24-28 cycles) could be modified to match different substrates (such as direct amplification of FTA paper); (d) complete profiles were observed with reaction volumes from 6.25 to 50 microL; (e) minimal impact was observed with variation of enzyme concentration; (f) full haplotypes were observed with 0.5-2x primer concentrations; however, relative yield between loci varied with concentration; (g) reduction of magnesium to 1mM (1.5 mM standard) resulted in minimal amplification, while only partial loss of yield was observed with 1.25 mM magnesium; (h) decreasing the annealing temperature by 2-4 degrees C did not generate artifacts or locus dropout and most laboratories observed full amplification with the annealing temperature increased by 2 degrees C and significant locus dropout with a 4 degrees C increase in annealing temperature; (i) amplification of individual loci with primers used in the multiplex produced the same alleles as observed with the multiplex amplification; (j) all laboratories observed full amplification with >or = 125 pg of male template with partial and/or complete profiles observed using 30-62.5 pg of DNA; (k) analysis of < or = 500 ng of female DNA did not yield amplification products; (l) the minor male component of a male/female mixture was observed with < or =1200-fold excess female DNA with the majority of alleles still observed with 10,000-fold excess female; (m) male/male mixtures produced full profiles from the minor contributor with 10-20-fold excess of the major contributor; (n) average stutter for each locus; (o) precision of sizing were determined; (p) human-specificity studies displayed amplification products only with some primate samples; and (q) reanalysis of 102 non-probative casework samples from 65 cases produced results consistent with original findings and in some instances additional identification of a minor male contributor to a male/female mixture was obtained. In general, the PowerPlex Y System was shown to have the sensitivity, specificity and reliability required for forensic DNA analysis.     

Validation of a male-specific, 12-locus fluorescent short tandem repeat (STR) multiplex

Y chromosome-specific short tandem repeat (Y-STR) analysis has become another widely accepted tool for human identification. The PowerPlex Y System is a fluorescent multiplex that includes the 12 loci: DYS19, DYS385a/b, DYS389I/II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438 and DYS439. This panel of markers incorporates the 9-locus European minimal haplotype (EMH) loci recommended by the International Y-STR User Group and the 11-locus set recommended by the Scientific Working Group on DNA Analysis Methods (SWGDAM). Described here are inter-laboratory results from 17 developmental validation studies of the PowerPlex Y System and include the following results: (a) samples distributed between laboratories and commercial standards produced expected and reproducible haplotypes; (b) use of common amplification and detection instruments were successfully demonstrated; (c) full profiles were obtained with standard 30 and 32 cycle amplification protocols and cycle number (24-28 cycles) could be modified to match different substrates (such as direct amplification of FTA paper); (d) complete profiles were observed with reaction volumes from 6.25 to 50 microL; (e) minimal impact was observed with variation of enzyme concentration; (f) full haplotypes were observed with 0.5-2x primer concentrations; however, relative yield between loci varied with concentration; (g) reduction of magnesium to 1mM (1.5 mM standard) resulted in minimal amplification, while only partial loss of yield was observed with 1.25 mM magnesium; (h) decreasing the annealing temperature by 2-4 degrees C did not generate artifacts or locus dropout and most laboratories observed full amplification with the annealing temperature increased by 2 degrees C and significant locus dropout with a 4 degrees C increase in annealing temperature; (i) amplification of individual loci with primers used in the multiplex produced the same alleles as observed with the multiplex amplification; (j) all laboratories observed full amplification with >or = 125 pg of male template with partial and/or complete profiles observed using 30-62.5 pg of DNA; (k) analysis of < or = 500 ng of female DNA did not yield amplification products; (l) the minor male component of a male/female mixture was observed with < or =1200-fold excess female DNA with the majority of alleles still observed with 10,000-fold excess female; (m) male/male mixtures produced full profiles from the minor contributor with 10-20-fold excess of the major contributor; (n) average stutter for each locus; (o) precision of sizing were determined; (p) human-specificity studies displayed amplification products only with some primate samples; and (q) reanalysis of 102 non-probative casework samples from 65 cases produced results consistent with original findings and in some instances additional identification of a minor male contributor to a male/female mixture was obtained. In general, the PowerPlex Y System was shown to have the sensitivity, specificity and reliability required for forensic DNA analysis.     

The extent of STR chimerism in different biological samples following bone marrow transplantation: A case report

Biological samples recovered from recipients of allogeneic haematopoietic stem cell transplant (HSCT) contain genetic material from both donor and him/herself. This chimeric condition can greatly complicate analysis of a DNA evidence and undermine its power of discrimination, as the specimens could be mistakenly identified as a mixed sample when in fact it originated from a single person. Profiling reference samples could help clarify the profile anomalies, however, the degree of mixture between host’s and donor’s genetic materials has been reported to vary depending on the tissue from which DNA were obtained. As a result, knowledge to select appropriate sources of reference samples that would most likely reveal the person’s pre- and post-transplant alleles becomes necessary to minimise any possible misunderstanding during the subsequent DNA profile interpretation and comparison. This work investigated the extent of chimerism present in different types of biological samples collected from an individual who had undergone a bone marrow transplant as a child (post-transplant interval, PTI >28 years). DNA profiles from buccal cells, saliva, hair roots, and fingernail clippings were generated using AmpFℓSTR™ Identifiler™ Plus/Direct PCR Amplification Kit. The donor’s STR profile was used to identify donor- and host-specific alleles (DSA and HSA, respectively), and relative donor chimerism (%Ch) of each marker was calculated. Results showed that the saliva sample contained the highest level of chimerism, with complete profile of donor being detected and the mean %Ch was 34.0 ± 4.5. Four out of eight DSA dropped out from the buccal cell profile, and the mean %Ch was 24.2 ± 1.7. Hair roots and fingernail clippings yielded single source profiles and only host’s original alleles were present. Except for the fingernail results, these observations agreed with many of the previous studies, which further demonstrated the need for raising awareness among forensic genetic laboratories regarding the type of reference samples that should be collected in future cases.     

TWGDAM validation of a nine-locus and a four-locus fluorescent STR multiplex system

The Gene Print PowerPlex 1.1/Amelogenin and FFFL Fluorescent STR Systems have been validated following the recommendations presented by the Technical Working Group on DNA Analysis Methods (TWGDAM). The PowerPlex 1.1/Amelogenin System supports simultaneous amplification of eight short tandem repeat loci and the Amelogenin gender identification marker. The loci D16S539, D7S820, D13S317, and D5S818 are labeled with fluorescein (FL) while the loci CSF1PO, TP0X, TH01, vWA and Amelogenin are labeled with carboxy-tetramethylrhodamine (TMR). The FFFL Multiplex System is composed of the loci F13A01, FESFPS, F13B, and LPL, each labeled with fluorescein. We have observed no overlap of alleles across loci labeled with an individual fluorescent dye. Samples of each system were amplified and labeled in a single reaction, separated by electrophoresis through a denaturing polyacrylamide gel, and amplified alleles detected using a Hitachi FMBIO Fluorescent Scanner. Alterations from the standard amplification protocols in cycle number and annealing temperature generally produced excellent results. In experiments testing sensitivity as little as 0.2 ng of DNA template could be detected. As expected, different body fluids from the same individuals generated identical DNA profile results. Template DNA derived from blood-strains deposited on a variety of matrix supports displayed robust amplification except for material derived from deposits on wood and Japanese orchid leaves. Mixtures of DNA templates could be interpreted with the minor component present in as little as ten percent of the total sample. Monoplex and multiplex amplifications produced identical amplified allele patterns, indicating that STR multiplex systems save template and increase efficiency in the amplification procedure without loss of quality. Analyses of genotype frequencies in African-American, Caucasian-American and Hispanic-American populations using all twelve loci were used to determine matching probabilities smaller than 1 in 1.14 x 10(8) and 1 in 2658 for the PowerPlex 1.1 and the FFFL Multiplex Systems, respectively. The matching probability achieved with the two systems combined is smaller than 1 in 3.03 x 10(11). The independence of alleles within loci was generally demonstrated by applying the exact test to demonstrate Hardy-Weinberg Equilibrium. All of the studies performed indicate that the PowerPlex 1.1/Amelogenin and FFFL Multiplex Systems are powerful, robust, and reliable investigative tools that can be used in the analysis of forensic samples.     

Laser microdissection separation of pure spermatozoa from epithelial cells for short tandem repeat analysis

Short tandem repeat (STR) analysis is a valuable tool in identifying the source of biological stains, particularly from the investigation of sexual assault crimes. Difficulties in analysis arise primarily in the interpretation of mixed genotypes when cell separation of the sexual assailant's sperm from the victim's cells is incomplete. The forensic community continues to seek improvements in cell separation methods from mixtures for DNA typing. The feasibility of applying laser microdissection (LMD) technology to precisely separate sexual assault cell mixtures by visual inspection coupled with laser dissection was assessed through three experiments. First, various histological stains were evaluated for use with LMD and DNA analysis. Second, different DNA isolation methods were evaluated on LMD-collected cells. Finally, STR analysis was performed on LMD-separated sperm cells from mixtures of semen and female buccal epithelial cells. The results indicated (a) hematoxylin/eosin staining performed best in its ability to differentiate sperm and epithelial cells while exhibiting the least negative effect on further downstream analysis; (b) both QIAamp and Lyse-N-Go methods were useful for recovery of DNA from LMD-collected sperm cells; and (c) LMD separation provided clear STR profiles of the male donor with the absence of any additional alleles from the female donor. This report describes an efficient, low-manipulation LMD method for the efficient separation of spermatozoa from two-donor sperm/epithelial cell mixtures.     

Developmental validation of the PowerPlex ESX 16 and PowerPlex ESX 17 Systems

We describe the developmental validation study performed on the PowerPlex^® ESX 16 (European Standard Extended 16) and the PowerPlex^® ESX 17 Systems, part of a suite of four new DNA profiling kits developed by Promega in response to the ENFSI and EDNAP groups’ call for new STR multiplexes for Europe. The PowerPlex^® ESX 16 System combines the 11 loci compatible with the UK National DNA Database, contained within the AmpFlSTR^® SGM Plus^® PCR Amplification Kit, with five additional loci: D2S441, D10S1248, D22S1045, D1S1656 and D12S391. The multiplex was designed to incorporate these five new loci as mini- and midi-STRs while maintaining the loci found in the AmpFlSTR^® SGM Plus^® kit as standard size. The PowerPlex^® ESX 17 System amplifies the same loci as the PowerPlex^® ESX 16 System, but with the addition of a primer pair for the SE33 locus. Tests were designed to address the developmental validation guidelines issued by the Scientific Working Group on DNA Analysis Methods (SWGDAM), and those of the DNA Advisory Board (DAB). Samples processed include DNA mixtures, PCR reactions spiked with inhibitors, a sensitivity series, and 306 United Kingdom donor samples to determine concordance with data generated with the AmpFlSTR^® SGM Plus^® kit. Allele frequencies from 242 white Caucasian samples collected in the United Kingdom are also presented. The PowerPlex^® ESX 16 and ESX 17 Systems are robust and sensitive tools, suitable for the analysis of forensic DNA samples. Full profiles were routinely observed with 62.5 pg of a fully heterozygous single source DNA template. In mixture analysis, a range of 52-95% of unique minor contributor alleles was observed at 19:1 mixture ratios where only 25 pg of the minor component was present. Improved sensitivity combined with the robustness afforded by smaller amplicons has substantially improved the quantity of information obtained from degraded samples, and the improved chemistry confers exceptional tolerance to high levels of laboratory prepared inhibitors.     

Novel cellular signatures for determining time since deposition for trace DNA evidence

With the increase in sensitivity of DNA profiling, questions about how and when the DNA was deposited have become a driving issue in forensic cases. To address this, we propose a novel method to determine time since deposition of trace DNA samples based on morphological and autofluorescence properties of individual epithelial cells which can change as the sample ages. To develop this signature, a series of trace DNA samples were generated by contact/handling a substrate and then allowed to age anywhere between one day and more than one year prior to collection. Imaging flow cytometry (IFC) was then used to characterize the morphology and autofluorescence profiles of individual cells within each sample followed by multivariate modelling and predictive classification.Resultsshowed that epithelial cell populations could be classified with high accuracy (∼90%) into one of three time-since-deposition groups: < 1 week, between 1 week and 2 months, and > 2months. Differences across age groups were largely driven by decreases in brightfield contrast and increases in the intensity of autofluorescence. To further test this approach for forensic casework, 47 individual donor cell populations spanning each time deposition group were classified blindly against the remaining data set. Samples containing at least 75 cells and a posterior probability greater than 0.90 showed classification accuracies ∼95%. Accuracies for individual time groups were 97% (<1 week), 92% (1week-2months), 98% (>2 months) with an average posterior probability for all time groups ∼0.96. This indicates that autofluorescence and morphological analyses may provide probative information regarding time since deposition for many types of trace DNA samples in forensic casework.     

基于下一代测序的全解析度STR分型研究进展与展望

下一代测序技术具有高通量、高速度、集成化、低成本等显著优势,近年来已在科研和临床诊断领域得到广泛应用,在法医遗传学领域亦具有重要应用前景。当前主流的STR分型方法仅关注序列的长度多态性,然而由于核心重复结构存在差异或扩增区段内存在SNP,序列长度相等的等位基因可能是具有遗传稳定性的完全不同的等位基因,此类STR序列多态性是个体识别或亲缘关系分析的宝贵资源。基于下一代测序的STR分型在现有数据输出方式基础上,允许进一步关注STR的序列多态性,对STR基因座进行全解析度分型,显著提升STR基因座的个体识别能力。本文以法医STR遗传标记和下一代测序技术为关注焦点,系统综述基于下一代测序的全解析度STR分型领域国际最新研究进展,深入探讨该技术在法医DNA实验室的实际应用潜力和可能面临的挑战,希冀对相关研究和实践提供参考。     

Internal Validation of the AmpFlSTR Yfiler™ Amplification Kit for Use in Forensic Casework

Abstract:  Y-chromosomal short-tandem repeat (Y-STR) amplification has been used in forensic casework at the Bureau of Criminal Apprehension (BCA) Forensic Science Laboratory since 2003. At that time, two separate amplifications were required to type the SWGDAM recommended loci (DYS19, DYS385a/b, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS438, and DYS439). The Yfiler™ kit coamplifies these loci as well as DYS437, DYS448, DYS456, DYS458, DYS635, and Y GATA H4. The Yfiler™ kit was validated following the internal validations outlined in the SWGDAM revised validation guidelines. Our studies show that 0.125 ng of male DNA will generate a complete 17 locus profile and that as little as 0.06 ng of male DNA yields an average of nine loci. In the male–male mixtures, a complete profile from the minor component was detected up to 1:5 ratio; most of the alleles of the minor component were detected at a 1:10 ratio and more than half the alleles of the minor component were detected at a 1:20 ratio. Complete YSTR profiles were obtained when 500 pg male DNA was mixed with female DNA at ratios up to 1:1000. At ratios of 1:5000 and 1:10,000 (male DNA to female DNA) inhibition of the YSTR amplification was evident. The YSTR results obtained for the adjudicated case samples gave significantly more probative information than the autosomal results. Our studies demonstrate that the Yfiler™ kit is extremely sensitive, does not exhibit cross-reactivity with female DNA, successfully types male DNA in the presence of overwhelming amounts of female DNA and is successful in typing actual forensic samples from adjudicated cases.     

广西地区壮族人群17个STR基因座遗传多态性研究

目的调查广西地区壮族人群17个STR基因座遗传多态性,为法医物证鉴定和群体遗传研究提供基础数据。方法收集2624份广西地区壮族人群无关个体样本采用Chelex-100提取样本DNA,用PowerPlex■18D System试剂盒进行PCR扩增及检测,计算群体遗传学参数。结果17个常染色体STR基因型分布均符合Hardy-Weinberg平衡定律(P>0.05),共检测出235个等位基因,971种基因型,累积个体识别率(TDP)为0.999999999999999,累积非父排除率(CPE)为0.999999772。结论17个STR基因座在广西地区壮族人群中具有较好的遗传多态性,可以用于法医学中个体识别和亲权鉴定,也可用于群体遗传学及法医学研究。     

A study on the effects of degradation and template concentration on the amplification efficiency of the STR Miniplex primer sets

In forensic DNA analysis, the samples recovered from the crime scene are often highly degraded leading to poor PCR amplification of the larger sized STR loci. To avoid this problem, we have developed STR markers with redesigned primer sequences called "Miniplexes" to produce smaller amplicons. To assess the effectiveness of these kits, we have tested these primer sets with enzymatically degraded DNA and compared the amplifications to a commercial kit. We also conducted sensitivity and peak balance studies of three Miniplex sets. Lastly, we report a case study on two human skeletal remain samples collected from different environmental conditions. In both types of degraded DNA, the Miniplex primer sets were capable of producing more complete profiles when compared to the larger sized amplicons from the commercial kit. Correct genotypes were obtained at template concentrations as low as 31 pg/25 microL. Overall, our data confirm that our redesigned primers can increase the probability of obtaining a usable profile in situations where standard kits fail.     

Quantifiler Human DNA Quantification Kit (Applied Biosystems) as a screening kit for DNA profiling

This study investigates the connection between the results of DNA quantification with Quantifiler Human DNA Quantification Kit (AB) and DNA profiling. For this purpose the DNA concentration of 3.068 routine casework samples was determined and DNA profiling was carried out. For discussion, depending on the specific DNA concentration, the samples were divided into four groups (0–5, 5–10, 10–30 and more then 30 pg/μl DNA) and the obtained number of full or partial profiles and the negative typing results was listed. Moreover group 1 (0–5 pg/μl DNA) results were subdivided and analysed more precisely. Based on the amount of 4% positive typing results in group 1 we decided to analyse every sample with quantification results >0 pg/μl DNA. A real cut-off no longer exists. Only samples showing 0 pg/μl on each result were sorted out.     

Extended PCR conditions to reduce drop-out frequencies in low template STR typing including unequal mixtures

Forensic laboratories employ various approaches to obtain short tandem repeat (STR) profiles from minimal traces (<100 pg DNA input). Most approaches aim to sensitize DNA profiling by increasing the amplification level by a higher cycle number or enlarging the amount of PCR products analyzed during capillary electrophoresis. These methods have limitations when unequal mixtures are genotyped, since the major component will be over-amplified or over-loaded. This study explores an alternative strategy for improved detection of the minor components in low template (LT) DNA typing that may be better suited for the detection of the minor component in mixtures. The strategy increases the PCR amplification efficiency by extending the primer annealing time several folds. When the AmpF?STR^® Identifiler^® amplification parameters are changed to an annealing time of 20 min during all 28 cycles, the drop-out frequency is reduced for both pristine DNA and single or multiple donor mock case work samples. In addition, increased peak heights and slightly more drop-ins are observed while the heterozygous peak balance remains similar as with the conventional Identifiler protocol. By this extended protocol, full DNA profiles were obtained from only 12 sperm heads (which corresponds to 36 pg of DNA) that were collected by laser micro dissection. Notwithstanding the improved detection, allele drop-outs do persist, albeit in lower frequencies. Thus a LT interpretation strategy such as deducing consensus profiles from multiple independent amplifications is appropriate. The use of extended PCR conditions represents a general approach to improve detection of unequal mixtures as shown using four commercially available kits (AmpF?STR^® Identifiler, SEfiler Plus, NGM and Yfiler). The extended PCR protocol seems to amplify more of the molecules in LT samples during PCR, which results in a lower drop-out frequency.