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- Harrison, Tabitha A., et al.
(författare)
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Genome-wide association study by colorectal carcinoma subtype
- 2018
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Ingår i: Cancer Research. - : American Association for Cancer Research. - 0008-5472 .- 1538-7445. ; 78:13
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Over 50 genetic variants have been associated with colorectal cancer (CRC) risk through genome-wide association studies (GWAS), yet these variants represent only a fraction of the total estimated heritability. CRC is a heterogenous disease with diverse tumor etiology. Assessing genetic risk in molecular subtypes may help to identify novel loci and characterize genetic risk among tumor subtypes. We used microsatellite instability (MSI), an established CRC classifier with etiological and therapeutic relevance, to define CRC subtypes for GWAS analyses. We conducted a case-case analysis to estimate odds ratios (OR) and 95% confidence intervals (CI) for association of genome-wide variants with microsatellite stable (MSS) versus unstable (MSI) carcinomas. We ran an inverse-variance weighted fixed-effects meta-analysis across GWAS in a discovery set of 4,163 population-based CRC cases with harmonized microsatellite instability (MSI) marker and imputed genotype data. For each analysis, we used log-additive logistic regression, adjusting for age, sex, and principal components to account for population substructure. We then followed up with replication of 102 SNPs that reached p-values less than 5x10-6 in 1,698 cases. A total of 845 (20.3%) cancer cases were microsatellite unstable in the discovery population and 174 (10.2%) were unstable in the replication population. No variants reached the genome-wide significance level of 5x10-8 in the discovery set. However, we identified two variants that reached a Bonferroni corrected p-value of 4.0x10-4 in the replication set. This included one variant in MLH1 (Replication: OR=1.74, 95% CI=1.53-1.98, p=1.63x10-5; Discovery+Replication: OR=1.45, 95% CI=1.37-1.54, p=9.76x10-11) and one variant in LOC105377645 (Replication: OR=1.70, 95% CI=1.49-1.94, p=5.13x10-5; Discovery+Replication: OR=1.45, 95% CI=1.37-1.54, p=9.76 x 10-11). The MLH1 gene is a DNA mismatch repair gene implicated in Lynch Syndrome, the hallmark of which is microsatellite instability. This is the first genome-wide scan to identify a common variant in MLH1 that is associated with CRC. This variant (minor allele frequency, MAF = 23% in this all European ancestry population) is located in the 5'-untranslated region of MLH1 and is thought to act as a long-range regulator of DCLK3, a potential tumor driver gene. The second variant, located in LOC105377645 with an MAF of 22%, is in an uncharacterized region of the genome and has not previously been implicated in cancer development. These findings suggest that accounting for molecular heterogeneity is important for discovery and characterization of genetic variants associated with CRC risk. We plan to run polytomous regression analyses, increase our sample size, and further investigate CRC subtypes by CIMP, BRAF mutation, KRAS mutation status.
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- Jacobs, Daniel I., et al.
(författare)
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Elucidating the molecular pathogenesis of familial glioma
- 2018
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Ingår i: Cancer Research. - : American Association for Cancer Research. - 0008-5472 .- 1538-7445. ; 78:13
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, the molecular characterization of sporadically arising diffuse gliomas has identified recurrent driving alterations and delineated molecularly and clinically distinct subclasses of disease. However, less is known about the molecular nature of gliomas that are familial in origin. To address this question, we integrated germline and somatic genomic data to characterize the molecular pathogenesis of 20 tumors arising in unrelated individuals with a family history of glioma collected through the Gliogene International Consortium. METHODS: FFPE tumor specimens were sectioned and reviewed to localize neoplastic tissue for DNA extraction. Library preparation, exome plus targeted capture, and paired-end sequencing on the Illumina HiSeq 2000 platform was performed at the Baylor College of Medicine Human Genome Sequencing Center. Single-nucleotide variants and indels were called with respect to germline DNA sequencing data for each case using MuTect2. Copy number profiling was performed on the Illumina HumanOmniExpress BeadChip and analyzed using GenomeStudio v2.0. Genotypes at known glioma risk polymorphisms were determined from germline DNA profiled on the Illumina Infinium OncoArray and rare, predicted deleterious germline mutations were identified from germline whole-exome sequencing data. RESULTS: Tumor exome sequencing was completed at an average read depth of 116X and we detected a median of 54 non-silent somatic mutations per tumor across the 20 tumors profiled. All three molecular subtypes of sporadic glioma were represented, including IDH-mutant, 1p/19q codeleted (n=3), IDH-mutant, 1p/19q intact (n=7), and IDH-wildtype tumors (n=10). Characteristic subtype-specific mutations and copy number alterations (e.g., TP53 and ATRX mutations among IDH-mutant, 1p/19q intact tumors) were observed, and the frequencies of recurrent alterations were comparable to sporadic glioma cases analyzed by The Cancer Genome Atlas. Notably, all 20 cases had alterations in genes regulating telomere length; 17 had acquired mutations in ATRX or the TERT promoter as typically seen in sporadic glioma, while three instead had germline mutations in telomere shelterin complex genes POT1 or TERF2. Frequencies of known common glioma risk alleles were similar to those among sporadic cases and correlations between risk alleles and specific somatic mutations were not observed. CONCLUSIONS: This study illustrates: 1) the complementarity of inherited and acquired alterations in driving gliomagenesis in some individuals with a familial predisposition to the disease; and 2) that the molecular characteristics of familial tumors profiled largely recapitulate what is known about sporadic glioma. In the majority of cases, the source of germline genetic susceptibility is not known but does not appear to be conferred by common risk polymorphisms.
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