Simultaneous mutation and copy number variation (CNV) detection by multiplex PCR-based GS-FLX sequencing

Multiplex Amplicon Quantification (MAQ), a fast and efficient method for the simultaneous detection of copy number alterations in neuroblastoma

Background

Cancer genomes display characteristic patterns of chromosomal imbalances, often with diagnostic and prognostic relevance. Therefore assays for genome-wide copy number screening and simultaneous detection of copy number alterations in specific chromosomal regions are of increasing importance in the diagnostic work-up of tumors.

Results

We tested the performance of Multiplex Amplicon Quantification, a newly developed low-cost, closed-tube and high-throughput PCR-based technique for detection of copy number alterations in regions with prognostic relevance for neuroblastoma. Comparison with array CGH and the established Multiplex Ligation-dependent Probe Amplification method on 52 neuroblastoma tumors showed that Multiplex Amplicon Quantification can reliably detect the important genomic aberrations.

Conclusion

Multiplex Amplicon Quantification is a low-cost and high-throughput PCR-based technique that can reliably detect copy number alterations in regions with prognostic relevance for neuroblastoma.

Haplotyping and copy number estimation of the highly polymorphic human beta-defensin locus on 8p23 by 454 amplicon sequencing

Background

The beta-defensin gene cluster (DEFB) at chromosome 8p23.1 is one of the most copy number (CN) variable regions of the human genome. Whereas individual DEFB CNs have been suggested as independent genetic risk factors for several diseases (e.g. psoriasis and Crohn's disease), the role of multisite sequence variations (MSV) is less well understood and to date has only been reported for prostate cancer. Simultaneous assessment of MSVs and CNs can be achieved by PCR, cloning and Sanger sequencing, however, these methods are labour and cost intensive as well as prone to methodological bias introduced by bacterial cloning. Here, we demonstrate that amplicon sequencing of pooled individual PCR products by the 454 technology allows in-depth determination of MSV haplotypes and estimation of DEFB CNs in parallel.

Results

Six PCR products spread over ~87 kb of DEFB and harbouring 24 known MSVs were amplified from 11 DNA samples, pooled and sequenced on a Roche 454 GS FLX sequencer. From ~142,000 reads, ~120,000 haplotype calls (HC) were inferred that identified 22 haplotypes ranging from 2 to 7 per amplicon. In addition to the 24 known MSVs, two additional sequence variations were detected. Minimal CNs were estimated from the ratio of HCs and compared to absolute CNs determined by alternative methods. Concordance in CNs was found for 7 samples, the CNs differed by one in 2 samples and the estimated minimal CN was half of the absolute in one sample. For 7 samples and 2 amplicons, the 454 haplotyping results were compared to those by cloning/Sanger sequencing. Intrinsic problems related to chimera formation during PCR and differences between haplotyping by 454 and cloning/Sanger sequencing are discussed.

Conclusion

Deep amplicon sequencing using the 454 technology yield thousands of HCs per amplicon for an affordable price and may represent an effective method for parallel haplotyping and CN estimation in small to medium-sized cohorts. The obtained haplotypes represent a valuable resource to facilitate further studies of the biomedical impact of highly CN variable loci such as the beta-defensin locus.

Deep sequencing to reveal new variants in pooled DNA samples

We evaluated massive parallel sequencing and long-range PCR (LRP) for rare variant detection and allele frequency estimation in pooled DNA samples. Exons 2 to 16 of the MUTYH gene were analyzed in breast cancer patients with Illumina's (Solexa) technology. From a pool of 287 genomic DNA samples we generated a single LRP product, while the same LRP was performed on 88 individual samples and the resulting products then pooled. Concentrations of constituent samples were measured with fluorimetry for genomic DNA and high-resolution melting curve analysis (HR-MCA) for LRP products. Illumina sequencing results were compared to Sanger sequencing data of individual samples. Correlation between allele frequencies detected by both methods was poor in the first pool, presumably because the genomic samples amplified unequally in the LRP, due to DNA quality variability. In contrast, allele frequencies correlated well in the second pool, in which all expected alleles at a frequency of 1% and higher were reliably detected, plus the majority of singletons (0.6% allele frequency). We describe custom bioinformatics and statistics to optimize detection of rare variants and to estimate required sequencing depth. Our results provide directions for designing high-throughput analyses of candidate genes.

Quantitative sequence analysis of FBN1 premature termination codons provides evidence for incomplete NMD in leukocytes

We improved, evaluated, and used Sanger sequencing for quantification of single nucleotide polymorphism (SNP) variants in transcripts and gDNA samples. This improved assay resulted in highly reproducible relative allele frequencies (e.g., for a heterozygous gDNA 50.0+/-1.4%, and for a missense mutation-bearing transcript 46.9+/-3.7%) with a lower detection limit of 3-9%. It provided excellent accuracy and linear correlation between expected and observed relative allele frequencies. This sequencing assay, which can also be used for the quantification of copy number variations (CNVs), methylations, mosaicisms, and DNA pools, enabled us to analyze transcripts of the FBN1 gene in fibroblasts and blood samples of patients with suspected Marfan syndrome not only qualitatively but also quantitatively. We report a total of 18 novel and 19 known FBN1 sequence variants leading to a premature termination codon (PTC), 26 of which we analyzed by quantitative sequencing both at gDNA and cDNA levels. The relative amounts of PTC-containing FBN1 transcripts in fresh and PAXgene-stabilized blood samples were significantly higher (33.0+/-3.9% to 80.0+/-7.2%) than those detected in affected fibroblasts with inhibition of nonsense-mediated mRNA decay (NMD) (11.0+/-2.1% to 25.0+/-1.8%), whereas in fibroblasts without NMD inhibition no mutant alleles could be detected. These results provide evidence for incomplete NMD in leukocytes and have particular importance for RNA-based analyses not only in FBN1 but also in other genes.

Direct multiplex sequencing (DMPS)--a novel method for targeted high-throughput sequencing of ancient and highly degraded DNA

Although the emergence of high-throughput sequencing technologies has enabled whole-genome sequencing from extinct organisms, little progress has been made in accelerating targeted sequencing from highly degraded DNA. Here, we present a novel and highly sensitive method for targeted sequencing of ancient and degraded DNA, which couples multiplex PCR directly with sample barcoding and high-throughput sequencing. Using this approach, we obtained a 96% complete mitochondrial genome data set from 31 cave bear (Ursus spelaeus) samples using only two 454 Life Sciences (Roche) GS FLX runs. In contrast to previous studies relying only on short sequence fragments, the overlapping portion of our data comprises almost 10 kb of replicated mitochondrial genome sequence, allowing for the unambiguous differentiation of three major cave bear clades. Our method opens up the opportunity to simultaneously generate many kilobases of overlapping sequence data from large sets of difficult samples, such as museum specimens, medical collections, or forensic samples. Embedded in our approach, we present a new protocol for the construction of barcoded sequencing libraries, which is compatible with all current high-throughput technologies and can be performed entirely in plate setup.

Filter-based hybridization capture of subgenomes enables resequencing and copy-number detection

To exploit contemporary sequencing technologies for targeted genetic analyses, we developed a hybridization enrichment strategy for DNA capture that uses PCR products as subgenomic traps. We applied this strategy to 115 kilobases of the human genome encompassing 47 genes implicated in cardiovascular disease. Massively parallel sequencing of captured subgenomic libraries interrogated 99.8% of targeted nucleotides >or=20 times ( approximately 40,000-fold enrichment), enabling sensitive and specific detection of sequence variation and copy-number variation.

Management of High-Throughput DNA Sequencing Projects: Alpheus

High-throughput DNA sequencing has enabled systems biology to begin to address areas in health, agricultural and basic biological research. Concomitant with the opportunities is an absolute necessity to manage significant volumes of high-dimensional and inter-related data and analysis. Alpheus is an analysis pipeline, database and visualization software for use with massively parallel DNA sequencing technologies that feature multi-gigabase throughput characterized by relatively short reads, such as Illumina-Solexa (sequencing-by-synthesis), Roche-454 (pyrosequencing) and Applied Biosystem's SOLiD (sequencing-by-ligation). Alpheus enables alignment to reference sequence(s), detection of variants and enumeration of sequence abundance, including expression levels in transcriptome sequence. Alpheus is able to detect several types of variants, including non-synonymous and synonymous single nucleotide polymorphisms (SNPs), insertions/deletions (indels), premature stop codons, and splice isoforms. Variant detection is aided by the ability to filter variant calls based on consistency, expected allele frequency, sequence quality, coverage, and variant type in order to minimize false positives while maximizing the identification of true positives. Alpheus also enables comparisons of genes with variants between cases and controls or bulk segregant pools. Sequence-based differential expression comparisons can be developed, with data export to SAS JMP Genomics for statistical analysis.