Discordant Alleles Research Articles

Optimization and Validation of Multimodular, Long-Range PCR–Based Next-Generation Sequencing Assays for Comprehensive Detection of Mutation in Tuberous Sclerosis Complex

The genetic diagnosis of tuberous sclerosis complex is difficult because of its broad spectrum of mutations. In addition to point mutations in coding regions, intragenic or chromosomal-level large deletions, deep intronic splicing mutations, and mosaic mutations represent a significant proportion of the mutations. In this study, multimodular, long-range PCR-based next-generation sequencing assays were optimized and validated using >100 samples with known TSC1 and TSC2 variants. Multiplex, long-range PCR covering the entire genomic region of both genes detected all 138 known variants; however, it also yielded false-positive results. Intragenic large deletions were detected with accurate breakpoint sequences. Chromosomal-level deletions were estimated by discordant allele segregation in the family and confirmed by DNA microarray. Deep intronic mutations were verified using a combination of long-range DNA PCR and full-length mRNA sequencing. DNA samples were mixed to simulate mosaic mutations, and most variants were detected but could not be distinguished from equivalently detected false-positive results. Repeated false-positive results were classified, and the strategy of selecting the common variants detected in the duplicate analysis and eliminating known false-positive results improved the sensitivity (85.2%) and positive predictive value (96.6%) of a 10% mosaic simulation. Long-range PCRbased next-generation sequencing is a highly versatile genetic test; however, confirmation tests remain necessary for clinical use because false-positive results cannot be completely eliminated from single experiments.

SweHLA: the high confidence HLA typing bio-resource drawn from 1000 Swedish genomes

There is a need to accurately call human leukocyte antigen (HLA) genes from existing short-read sequencing data, however there is no single solution that matches the gold standard of Sanger sequenced lab typing. Here we aimed to combine results from available software programs, minimizing the biases of applied algorithm and HLA reference. The result is a robust HLA population resource for the published 1000 Swedish genomes, and a framework for future HLA interrogation. HLA 2nd-field alleles were called using four imputation and inference methods for the classical eight genes (class I: HLA-A, HLA-B, HLA-C; class II: HLA-DPA1, HLA-DPB1, HLA-DQA1, HLA-DQB1, HLA-DRB1). A high confidence population set (SweHLA) was determined using an n−1 concordance rule for class I (four software) and class II (three software) alleles. Results were compared across populations and individual programs benchmarked to SweHLA. Per gene, 875 to 988 of the 1000 samples were genotyped in SweHLA; 920 samples had at least seven loci called. While a small fraction of reference alleles were common to all software (class I = 1.9% and class II = 4.1%), this did not affect the overall call rate. Gene-level concordance was high compared to European populations (>0.83%), with COX and PGF the dominant SweHLA haplotypes. We noted that 15/18 discordant alleles (delta allele frequency >2) were previously reported as disease-associated. These differences could in part explain across-study genetic replication failures, reinforcing the need to use multiple software solutions. SweHLA demonstrates a way to use existing NGS data to generate a population resource agnostic to individual HLA software biases.

Sequence variation observed in 27 Y-STR markers with U.S. population samples

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

Performance Characteristics and Validation of Next-Generation Sequencing for Human Leucocyte Antigen Typing

High-resolution human leukocyte antigen (HLA) matching reduces graft-versus-host disease and improves overall patient survival after hematopoietic stem cell transplant. Sanger sequencing has been the gold standard for HLA typing since 1996. However, given the increasing number of new HLA alleles identified and the complexity of the HLA genes, clinical HLA typing by Sanger sequencing requires several rounds of additional testing to provide allele-level resolution. Although next-generation sequencing (NGS) is routinely used in molecular genetics, few clinical HLA laboratories use the technology. The performance characteristics of NGS HLA typing using TruSight HLA were determined using Sanger sequencing as the reference method. In total, 211 samples were analyzed with an overall accuracy of 99.8% (2954/2961) and 46 samples were analyzed for precision with 100% (368/368) reproducibility. Most discordant alleles were because of technical error rather than assay performance. More important, the ambiguity rate was 3.5% (103/2961). Seventy-four percentage of the ambiguities were within the DRB1 and DRB4 loci. HLA typing by NGS saves approximately $6000 per run when compared to Sanger sequencing. Thus, TruSight HLA assay enables high-throughput HLA typing with an accuracy, precision, ambiguity rate, and cost savings that should facilitate adoption of NGS technology in clinical HLA laboratories.

Comprehensive investigation in patients affected by sperm macrocephaly and globozoospermia.

The aim of this study was to provide a comprehensive genetic/phenotypic characterization of subjects suffering infertility owing to sperm macrocephaly (n = 3) or globozoospermia (n = 9) and to investigate whether the patients' genetic status was correlated with the alteration of various sperm parameters. AURKC was sequenced in case of sperm macrocephaly while the DPY19L2 status has been analyzed by multiple approaches including a novel qPCR-based copy number assay in case of globozoospermia. Globozoospermic patients were also analyzed for SPACA1, a novel candidate gene herein tested for the first time in humans. The effect of the patients' genetic status was interrogated by implementing the molecular screening with the characterization of several sperm parameters: (i) routine sperm analysis, integrated with transmission electron microscopy; (ii) sperm fluorescent in situ hybridization (FISH) analysis; (iii) sperm DNA fragmentation (DF) analysis. Moreover, for the first time, we performed microsatellite instability analysis as a marker of genome instability in men with sperm macrocephaly and globozoospermia. Finally, artificial reproductive technology (ART) history has been reported for those patients who underwent the treatment. Macrocephalic patients had an AURKC mutation and >89% tetraploid, highly fragmented spermatozoa. DPY19L2 was mutated in all patients with >80% globozoospermia: the two homozygous deleted men and the compound heterozygous showed the severest phenotype (90-100%). The newly developed qPCR method was fully validated and has the potential of detecting also yet undiscovered deletions. DPY19L2 status is unlikely related to FISH anomalies and DF, although globozoospermic men showed a higher disomy rate and DF compared with internal reference values. No patient was mutated for SPACA1. Our data support the general agreement on the negative correlation between macro/globozoospermia and conventional intracytoplasmic sperm injection outcomes. Microsatellites were stable in all patients analyzed. The comprehensive picture provided on these severe phenotypes causing infertility is of relevance in the management of patients undergoing ART.

12-OR

Aim An HLA class II next generation sequencing (NGS) method, on the Illumina MiSeq platform with software we developed to extract HLA typing from the raw data, was applied to a cohort of hematopoietic stem cell transplant donors and recipients. Methods NGS data for DRB1/3/4/5, DQA1 and DQB1 included exons 2 and 3 and DPA1, DPB1 data was from exon 2. Legacy DRB1 and DQB1 typing of the transplant cohort was provided by the Seattle Cancer Care Alliance Clinical Immunogenetics Laboratory (CIL) and the Fred Hutchinson Cancer Research Center Clinical Research Database according to IRB-approved research protocols. The legacy HLA data was generated by various serology, SSP, SSOP and SBT methods. Discrepancy resolution involved review of CIL records and the NGS raw data and adjustments in the NGS analysis software. Results DRB1 NGS genotyping was available for 2436 specimens, and identified 53 alleles, including 10 of DRB1*04 alleles, 7 of *14, 6 each of *08, *13 and *15, 5 of *11, 3 each of *01 and *03, 2 of *12 and *16, and *07:01, *09:01 and *10:01. DQB1 NGS typing, available for 2444 specimens, identified 26 alleles, including 9 of DQB1*06, 6 of *03, 5 of *05, and 3 each of *02 and *04. These included a new DRB1 allele and 5 novel DQB1 alleles. Comparison of legacy and NGS data revealed 38 (0.78%) discordant DRB1 allele assignments, including 9 legacy data transcription errors, 8 legacy discordant alleles, and 21 of false homozygosity in the NGS results. At DQB1 the 283 (5.8%) discordant alleles included 4 legacy transcription errors, 24 legacy miscalls with exon 2 disparity and 208 legacy disparities involving exon 3 (not tested in legacy). NGS results exhibited 7 allele miscalls, 16 “script” errors involving exon 3 polymorphism, and 4 “rule set” errors in failure to detect DQB1*05:04. Conclusions The less than 1% NGS miscalls at DRB1 (0.43%) and DQB1 (0.55%) and the detection of novel allele sequences demonstrates the robust reliability and sensitivity of this next generation sequencing technology. Smith: Scisco Genetics: Consultant. Pereira: Scisco Genetics: Science Med Advisor. Geraghty: Scisco Genetics: Science Med Advisor.

Clinical next generation sequencing (NGS) of fine needle aspiration (FNA) biopsies in non-small cell lung (NSCLC) and pancreatic cancers.

11100 Background: FNA is a common diagnostic procedure for the evaluation of pulmonary and pancreatic masses. We sought to determine whether NGS could be performed on these small specimens and to characterize heterogeneity across classes of genomic alterations (GA) in a subset of paired FNA and matched resected primary tumors. Methods: DNA was isolated from formalin fixed paraffin embedded (FFPE) sections of FNA cell blocks using 40µm total sections for NSCLC and 20µm total sections for pancreatic cancers in a CLIA-certified lab (Foundation Medicine). DNA sequencing was performed for 3,320 exons of 182 cancer-related genes and 37 introns of 14 genes frequently rearranged in cancer on indexed, adaptor ligated, hybridization-captured libraries to a median depth of 931x for the NSCLC and 416x for the pancreatic FNAs. Results: Genomic profiles were successfully generated from 19/19 of the NSCLC and 22/23 of the pancreatic FNA cases. We found 97 GA in the 19 NSCLC FNAs (range 2-9, average 5.1 GA per patient). 68% of the patients had GA in TP53 and 21% in KRAS. Only 16% (3/19) patients did not exhibit an actionable alteration. We found 99 GA in the 23 pancreatic cancer FNAs (range 0-12, average 4.3 per patient). 74% of the patients had GA in KRAS. There was 94% concordance of GA found in 4 matched FNA and primary tumor pairs for the pancreatic cases. For the single discordance, manual inspection of the reads of the discordant allele indicated evidence of loss of heterozygosity. Conclusions: NGS can be reliably performed on small FNA samples processed into cell blocks, and the GA discovered significantly correlates with the GA found in matched primary tumors. This study demonstrates the feasibility of NGS in analyzing FNA samples and further broadens the spectrum of commonly encountered specimen types to which this approach can be successfully applied.

Variants observed for STR locus SE33: A concordance study

Discordance of STR typing results can be expected between kits that employ different primers for amplification. The complex motif of the SE33 locus and its flanking regions can contribute to the degree of discordant results. Sequence-dependent conformational changes can manifest as length differences under certain electrophoretic conditions and/or use of different primers. The AmpFlSTR® NGM SElect™ PCR Amplification Kit (Life Technologies, Carlsbad, CA), PowerPlex® ESX 17 system (Promega Corporation, Madison, WI), and PowerPlex® ESI 17 system (Promega Corporation) were compared for concordance of allele calls for the SE33 marker in selected samples. A total of 16 samples were identified that were discordant at one of the SE33 alleles by an apparent one nucleotide in size. While the ESX 17 and NGM SElect™ kits yielded concordant results for these 16 samples, the ESI 17 kit generated alleles that differed. The discordant alleles were observed in individuals of African and European descent. Sequence analysis revealed that the one-base difference in size is not due to an indel but is instead the result of a single nucleotide polymorphism (SNP) in the flanking region of the SE33 repeat region. Three different SNPs were observed, one of which is novel.Although these migration anomalies were observed only with the ESI 17 kit, one cannot preclude that a similar phenomenon may occur with the other kits as data sets increase. The type and degree of discordance of STR allele calls among STR kits is an important issue when comparing STR profiles among laboratories and when determining search parameters for identifying candidate associations in national databases.

Identification and secondary structure analysis of a region affecting electrophoretic mobility of the STR locus SE33

SE33 is one of the most informative markers in forensic use due to its high power of discrimination. During the course of developing the AmpFℓSTR® NGM SElect™ PCR Amplification Kit several SE33 primer designs were screened with one primer pair yielding a high frequency of discordant alleles when compared to the AmpFℓSTR® SEfiler Plus™ PCR Amplification Kit. This discordance was mostly specific to samples of African descent with an estimated frequency of 5.1% and was a result of a mobility shift of approximately +0.84nt. The sequence analysis of the affected alleles revealed that the only difference from the wild type sequence was a single nucleotide polymorphism (SNP) outside of the SE33 repeat but within the amplicon of this particular set of experimental primers. In total, we identified three different SNPs all within 9nt of each other, each of which could cause the mobility shift individually. Further characterization of this region via site directed mutagenesis and thermostability measurements strongly suggests that this polymorphic region contains a secondary structure that, when disrupted due to the presence of a variant SNP, results in a mobility shift relative to the wild type sequence. To overcome this problem, the SE33 primers used in the final configuration of the NGM SElect™ Kit avoided the amplification of this polymorphic region yielding in turn results highly concordant with the SEfiler Plus™ Kit.

Inclusion Probabilities and Dropout

Recent discussions on a forensic discussion group highlighted the prevalence of a practice in the application of inclusion probabilities when dropout is possible that is of significant concern. In such cases, there appears to be an unpublished practice of calculation of an inclusion probability only for those loci at which the profile of interest (hereafter the suspect) is fully included among the alleles present in the crime scene sample and to omit those loci at which the suspect has alleles that are not fully represented among the alleles in the mixture. The danger is that this approach may produce apparently strong evidence against a surprisingly large fraction of noncontributors. In this paper, the risk associated with the approach of ignoring loci with discordant alleles is assessed by simulation.

Molecular Determination of Primary Versus Metastatic Squamous Cell Carcinoma (SCC) of the Lung in the Context of SCC of the Head and Neck (H/N)

Patients with SCC H/N are at a high risk of developing lung SCC. Given similar histology, the distinction between metastatic and primary SCC is difficult. Thus, molecular methods may be clinically useful to evaluate tumor relatedness. We previously showed that assessment of microsatellite allelic variation can be utilized to discriminate multiple primary versus metastatic SCC of H/N. The goal of this study was to refine this methodology using fluorescent‐labeled primers with automated detection. Genomic DNA was extracted from paraffin‐embedded tumor samples from nine patients who had undergone resection of SCC of both the H/N and lung. Comparison was made between microsatellite PCR with PAGE analysis versus fluorescent product detection. Both methods yielded interpretable results. Metastatic lung SCC were characterized by either identical alleles or allelic losses as compared to SCC H/N, while metachronous primary SCC lung were characterized by discordant alleles to the SCC H/N. Fluorescent product detection is able to detect some allelic discordant which is not detectable by PAGE analysis. Fluorescent product detection is sensitive and high‐throughput. The results confirm that molecular methods can distinguish primary vs. metastatic SCC of the lung in the context of SCC H/N. Accurate characterization of these lesions may significantly impact clinical management strategies for these patients.

Analysis of Six Genetic Risk Factors Highly Associated with AMD in the Region SurroundingARMS2andHTRA1on Chromosome 10, Region q26

Purpose. To determine the relationship of six genetic variants (rs10490924, rs3750848, del443ins54, rs3793917, rs11200638, and rs932275) localized to the ARMS2-HTRA1 region of chromosome 10, region q26, as risk factors for age-related macular degeneration (AMD), to define the haplotype structure of these six loci, and to confirm their genetic association with the disease. Methods. Caucasian patients (n = 482) were stratified into categories based on AREDS (Age-Related Eye Disease Study) grading criteria (groups 0 and 1 served as the control, groups 3 and 4 contained subjects with AMD, and group 2 was excluded from the analysis). The six genetic variants in the ARMS2-HTRA1 region were genotyped and analyzed both independently and as a joint haplotype for association in subjects with disease (n = 291) compared with the control (n = 191). Results. The six high-risk alleles all showed a statistically significant association with AMD (the most significant SNP was rs10490924 [P < or = 3.31 x 10(-5), OR = 1.86]; the least significant SNP was rs932275 [P < or = 9.15 x 10(-5), OR = 1.78]). Multimarker analysis revealed that all six markers were in strong linkage disequilibrium with each other, and the two major haplotypes that captured >98% of the genetic variation in the region were both significantly associated with the disease: One increased the risk of AMD and contained only risk alleles (P < or = 2.20 x 10(-5)), and the other haplotype decreased the risk of AMD and contained only wild-type alleles (P < or = 6.81 x 10(-5)). Furthermore, 36 individuals comprising both cases and controls were identified outside of these two major haplotypes, with at least one discordant marker. Conclusions. The results replicate the previously reported association between the high-risk alleles and AMD and independently confirm, for the first time, an association with AMD and the indel (del443ins54) polymorphism in a Caucasian population. Two major haplotypes that are associated with AMD and many minor novel haplotypes were identified. The novel haplotypes, identified from 36 cases and controls with discordant alleles spanning the ARMS2-HTRA1 region provide unique opportunities to gauge the relative phenotypic contributions of each of these genetic risk factors. With the identification of more discordant patients in the future, it may be possible to resolve the ongoing controversy as to which of the risk alleles and genes (ARMS2 vs. HTRA1) has the greatest impact on disease susceptibility. Future work should include the analysis of larger and more diverse populations, to further define the linkage structure of the region with a focus on phenotypic effects on AMD of the various haplotypes involving 10q26, as well as a functional analysis of the normal ARMS2 protein.

Hunting for disease genes in multi-functional diseases.

Disease genes may be identified through functional, positional, and candidate gene approaches. Although extensive and often labor-intensive studies such as family linkage analysis, functional investigation of gene products and genome database searches are usually involved, thousands of human disease genes, especially for monogenic diseases with Mendelian transmission, have been identified. However, in diseases caused by more than one gene, or by a combination of genetic and environmental factors, identification of the genes is even more difficult. Common examples include atherosclerosis, cancer, Alzheimer's disease, asthma, diabetes, glaucoma, and age-related macular degeneration. There have been conflicting reports on the roles of associated genes. Even with population-based case-control studies and new statistical methods such as the sib-ship disequilibrium test and the discordant alleles test, there is no agreement on whether alpha2-macroglobulin (A2M) is a gene for Alzheimer's disease. Another example is the inconsistent association between age-related macular degeneration and ATP-binding cassette transporter (ABCR). Ethnic variation causes further complications. In our investigation of LDL-receptor variants in familial hypercholesterolemia, and the trabecular meshwork inducible glucocorticoid response protein, or myocillin (TIGR-MYOC) mutation pattern in primary open angle glaucoma, we did find dissimilar results in Chinese compared to Caucasians. New information from the Human Genome Project and advancements in technologies will aid the search for and confirm identification of disease genes despite such challenges.

Cytonuclear genetic architecture in mosquitofish populations and the possible roles of introgressive hybridization

AbstractSpatial genetic structure in populations of mosquitofish (Gambusia) sampled throughout the south‐eastern United States was characterized using mitochondrial (mt) DNA and allozyme markers. Both sets of data revealed a pronounced genetic discontinuity (along a broad path extending from south‐eastern Mississippi to north‐eastern Georgia) that corresponds to a recently recognized distinction between the nominal forms G. affinis to the west and G. holbrooki to the east. However, several populations from the general contact region exhibited unusual allelic associations in high frequency, suggestive of evolutionary processes within a zone of introgressive hybridization. These involve: (i) cytonuclear profiles representing combinations of nuclear and mitochondrial genotypes that tended to be more nearly species‐specific and concordant elsewhere; and (ii) significant nuclear gametic disequilibria, perhaps attributable to positive assortative mating and/or differential fitnesses of homospecific vs. recombinant genotypes. However, outside this suspected hybrid region, ‘heterospecific’ genetic markers also appeared in low frequency, thus complicating interpretations. These discordant alleles on a broader geographic scale may reflect: (a) the retention of polymorphisms from an ancestral gene pool; (b) occasional evolutionary convergence (especially with respect to electrophoretic mobility of allozyme alleles); (c) the ‘footprints’ of a moving hybrid zone; or (d) differential introgressive penetrance across the current hybrid region.

Estimation of the frequency of isoform-genotype discrepancies at the apolipoprotein E locus in heterozygotes for the isoforms.

Estimates of the impact of apolipoprotein E (apo E) alleles coding for the three common isoforms on plasma lipid levels assume genetic homogeneity among the genotype classes. To test this assumption, we have determined the apo E genotype at the two common polymorphic sites (amino acids 112 and 158) by DNA amplification and hybridisation with allele-specific oligoprobes, in 195 unrelated Caucasian participants of the Rochester Family Heart Study previously classified as heterozygotes by isoelectric focusing (IEF). Fourteen discordant samples were initially detected. Repeat typing of these samples by both methods resolved nine discrepancies and analysis of additional blood samples from the remaining five individuals eliminated a further four discrepancies. The only truly discordant allele was found in a female subject who had an E3 isoform with the common E2 (Cys112, Cys158) genotype. Transmission of this allele from the mother was demonstrated. From these results, we estimate the frequency of discrepancies between isoforms and common genotypes to be 0.25% in this population. Allele misclassification was caused by poor amplification of the DNA in six samples and superimposition of glycosylated and nonglycosylated apo E isoforms on isoelectric focusing gels in five samples. We conclude that the assumption of genetic homogeneity among genotype classes is valid and that misclassification due to technical difficulties is more frequent than true discordancies.