Targeted Exome Sequencing Outcome Variations of Colorectal Tumors within and across Two Sequencing Platforms

Driver genes exome sequencing reveals distinct variants in African Americans with colorectal neoplasia

BACKGROUND

Colorectal cancer (CRC) is the third leading cause of cancer-related deaths in the United States. African Americans are disproportionately affected by CRC. Our hypothesis is that driver genes with known and novel mutations have an impact on CRC outcome in this population. Therefore, we investigated the variants' profiles in a panel of 15 CRC genes.

PATIENTS & METHODS

Colorectal specimens (n=140) were analyzed by targeted exome sequencing using an Ion Torrent platform. Detected variants were validated in 36 samples by Illumina sequencing. The novel status of the validated variants was determined by comparison to publicly available databases. Annotated using ANNOVAR and in-silico functional analysis of these variants were performed to determine likely pathogenic variants.

RESULTS

Overall, 121 known and novel variants were validated: APC (27%), AMER1 (3%), ARID1 (7%), MSH3 (12%), MSH6 (10%), BRAF (4%), KRAS (6%), FBXW7 (4%), PIK3CA (6%), SMAD4 (5%), SOX9 (2%), TCF7L2 (2%), TGFBR2 (5%), TP53 (7%). From these validated variants, 12% were novel in 8 genes (AMER1, APC, ARID1A, BRAF, MSH6, PIK3CA, SMAD4, and TCF7L2). Of the validated variants, 23% were non-synonymous, 14% were stopgains, 24% were synonymous and 39% were intronic variants.

CONCLUSION

We here report the specifics of variants' profiles of African Americans with colorectal lesions. Validated variants showed that Tumor Suppressor Genes (TSGs) APC and ARID1 and DNA Mismatch repair (MMR) genes MSH3 and MSH6 are the genes with the highest numbers of validated variants. Oncogenes KRAS and PIK3CA are also altered and likely participate in the increased proliferative potential of the mutated colonic epithelial cells in this population.

[Massive parallel sequencing for molecular-genetic diagnosis of mental retardation]

Gene mutations occur with high frequency in children with mental retardation. Standard diagnostic methods, such as TMS, Sanger's sequencing of individual genes, MLPA analysis of deletions, and investigation of methylation status in Martin-Bell syndrome are not informative in the majority of cases that hampered further diagnostic efforts. Massive parallel sequencing (MPS) allowed physicians to continue diagnostic search in previously undiagnosed cases and to find molecular causes of disease. MPS permits to discover a large number of new genes and understand the pathogenesis of mental retardation and brain development more deeply. It became possible to perform prenatal and pre-implantation diagnostics. However, big data generate big problems with their interpretation the genetic counselor faces with. This review reflects the advantages and disadvantages of MPS. Different variants of MPS, including gene panels, whole exome and whole genome sequencing as well as sequencing of trios, are described. In addition, the authors discuss the difficulties of interpretation of the results and recommendations for obtaining the most accurate results.

Species classifier choice is a key consideration when analysing low-complexity food microbiome data

BACKGROUND

The use of shotgun metagenomics to analyse low-complexity microbial communities in foods has the potential to be of considerable fundamental and applied value. However, there is currently no consensus with respect to choice of species classification tool, platform, or sequencing depth. Here, we benchmarked the performances of three high-throughput short-read sequencing platforms, the Illumina MiSeq, NextSeq 500, and Ion Proton, for shotgun metagenomics of food microbiota. Briefly, we sequenced six kefir DNA samples and a mock community DNA sample, the latter constructed by evenly mixing genomic DNA from 13 food-related bacterial species. A variety of bioinformatic tools were used to analyse the data generated, and the effects of sequencing depth on these analyses were tested by randomly subsampling reads.

RESULTS

Compositional analysis results were consistent between the platforms at divergent sequencing depths. However, we observed pronounced differences in the predictions from species classification tools. Indeed, PERMANOVA indicated that there was no significant differences between the compositional results generated by the different sequencers (p = 0.693, R² = 0.011), but there was a significant difference between the results predicted by the species classifiers (p = 0.01, R² = 0.127). The relative abundances predicted by the classifiers, apart from MetaPhlAn2, were apparently biased by reference genome sizes. Additionally, we observed varying false-positive rates among the classifiers. MetaPhlAn2 had the lowest false-positive rate, whereas SLIMM had the greatest false-positive rate. Strain-level analysis results were also similar across platforms. Each platform correctly identified the strains present in the mock community, but accuracy was improved slightly with greater sequencing depth. Notably, PanPhlAn detected the dominant strains in each kefir sample above 500,000 reads per sample. Again, the outputs from functional profiling analysis using SUPER-FOCUS were generally accordant between the platforms at different sequencing depths. Finally, and expectedly, metagenome assembly completeness was significantly lower on the MiSeq than either on the NextSeq (p = 0.03) or the Proton (p = 0.011), and it improved with increased sequencing depth.

CONCLUSIONS

Our results demonstrate a remarkable similarity in the results generated by the three sequencing platforms at different sequencing depths, and, in fact, the choice of bioinformatics methodology had a more evident impact on results than the choice of sequencer did.

Targeted exome sequencing reveals distinct pathogenic variants in Iranians with colorectal cancer

PURPOSE

Next Generation Sequencing (NGS) is currently used to establish mutational profiles in many multigene diseases such as colorectal cancer (CRC), which is on the rise in many parts of the developing World including, Iran. Little is known about its genetic hallmarks in these populations.

AIM

To identify variants in 15 CRC-associated genes in patients of Iranian descent.

RESULTS

There were 51 validated variants distributed on 12 genes: 22% MSH3 (n = 11/51), 10% MSH6 (n = 5/51), 8% AMER1 (n = 4/51), 20% APC (n = 10/51), 2% BRAF (n = 1/51), 2% KRAS (n = 1/51), 12% PIK3CA (n = 6/51), 8% TGFβR2A (n = 4/51), 2% SMAD4 (n = 1/51), 4% SOX9 (n = 2/51), 6% TCF7L2 (n = 3/51), and 6% TP53 (n = 3/51). Most known and distinct variants were in mismatch repair genes (MMR, 32%) and APC (20%). Among oncogenes, PIK3CA was the top target (12%).

MATERIALS AND METHODS

CRC specimens from 63 Shirazi patients were used to establish the variant' profile on an Ion Torrent platform by targeted exome sequencing. To rule-out technical artifacts, the variants were validated in 13 of these samples using an Illumina NGS platform. Validated variants were annotated and compared to variants from publically available databases. An in-silico functional analysis was performed. MSI status of the analyzed samples was established.

CONCLUSION

These results illustrate for the first time CRC mutational profile in Iranian patients. MSH3, MSH6, APC and PIK3CA genes seem to play a bigger role in the path to cancer in this population. These findings will potentially lead to informed genetic diagnosis protocol and targeted therapeutic strategies.

Next-generation sequencing: recent applications to the analysis of colorectal cancer

Since the establishment of the Sanger sequencing method, scientists around the world focused their efforts to progress in the field to produce the utmost technology. The introduction of next-generation sequencing (NGS) represents a revolutionary step and promises to lead to massive improvements in our understanding on the role of nucleic acids functions. Cancer research began to use this innovative and highly performing method, and interesting results started to appear in colorectal cancer (CRC) analysis. Several studies produced high-quality data in terms of mutation discovery, especially about actionable or less frequently mutated genes, epigenetics, transcriptomics. Analysis of results is unveiling relevant perspectives aiding to evaluate the response to therapies. Novel evidences have been presented also in other directions such as gut microbiota or CRC circulating tumor cells. However, despite its unquestioned potential, NGS poses some issues calling for additional studies. This review intends to offer a view of the state of the art of NGS applications to CRC through examination of the most important technologies and discussion of recent published results.

Distinctive DNA mismatch repair and APC rare variants in African Americans with colorectal neoplasia

PURPOSE

African Americans have a higher incidence and mortality from colorectal cancer. This disparity might be due, in part, to the type of mutations in driver genes. In this study, we examined alterations specific to APC, MSH3, and MSH6 genes using targeted exome sequencing to determine distinctive variants in the course of neoplastic transformation.

EXPERIMENTAL DESIGN

A total of 140 African American colon samples (30 normal, 21 adenomas, 33 advanced adenomas and 56 cancers) were used as our discovery set on an Ion Torrent platform. A 36 samples subset was resequenced on an Illumina platform for variants' validation. Bioinformatics analyses were performed and novel validated variants are reported.

RESULTS

Two novel MSH6 variants were validated and mapped to the MutS-V region near the MSH2 binding site. For MSH3, 4 known variants were validated and were located in exon 10 (3 non-synonymous) and exon 18 (1 synonymous). As for APC, 20 variants were validated with 4 novel variants: 3 stopgain and 1 non-synonymous. These variants mapped prior to and on the Armadillo repeats region, to the 15-amino acid repeat region, and to the 20-amino acid repeats region, respectively.

CONCLUSION

We defined novel variants that target DNA mismatch repair and APC genes in African Americans with colorectal lesions. A greater frequency of variants in genes encoding DNA mismatch repair functions and APC likely plays major roles in colorectal cancer initiation and higher incidence of the disease in African Americans.