Inherited cancer predisposing mutations in patients with therapy-related myeloid neoplasms

Some patients with therapy-related myeloid neoplasms (t-MN) may have unsuspected inherited cancer predisposition syndrome (CPS). We propose a set of clinical criteria to identify t-MN patients with high risk of CPS (HR-CPS). Among 225 t-MN patients with an antecedent non-myeloid malignancy, our clinical criteria identified 52 (23%) HR-CPS patients. Germline whole-exome sequencing identified pathogenic or likely pathogenic variants in 10 of 27 HR-CPS patients compared to 0 of 9 low-risk CPS patients (37% vs. 0%, p = 0.04). These simple clinical criteria identify t-MN patients most likely to benefit from genetic testing for inherited CPS.

Specifications of the ACMG/AMP variant interpretation guidelines for germline TP53 variants

Germline pathogenic variants in TP53 are associated with Li-Fraumeni syndrome, a cancer predisposition disorder inherited in an autosomal dominant pattern associated with a high risk of malignancy, including early-onset breast cancers, sarcomas, adrenocortical carcinomas, and brain tumors. Intense cancer surveillance for individuals with TP53 germline pathogenic variants is associated with reduced cancer-related mortality. Accurate and consistent classification of germline variants across clinical and research laboratories is important to ensure appropriate cancer surveillance recommendations. Here, we describe the work performed by the Clinical Genome Resource TP53 Variant Curation Expert Panel (ClinGen TP53 VCEP) focused on specifying the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) guidelines for germline variant classification to the TP53 gene. Specifications were developed for 20 ACMG/AMP criteria, while nine were deemed not applicable. The original strength level for the 10 criteria was also adjusted due to current evidence. Use of TP53-specific guidelines and sharing of clinical data among experts and clinical laboratories led to a decrease in variants of uncertain significance from 28% to 12% compared with the original guidelines. The ClinGen TP53 VCEP recommends the use of these TP53-specific ACMG/AMP guidelines as the standard strategy for TP53 germline variant classification.

Real-world Evidence of Diagnostic Testing and Treatment Patterns in US Patients With Breast Cancer With Implications for Treatment Biomarkers From RNA Sequencing Data

OBJECTIVE/BACKGROUND

We performed a retrospective analysis of longitudinal real-world data (RWD) from patients with breast cancer to replicate results from clinical studies and demonstrate the feasibility of generating real-world evidence. We also assessed the value of transcriptome profiling as a complementary tool for determining molecular subtypes.

METHODS

De-identified, longitudinal data were analyzed after abstraction from records of patients with breast cancer in the United States (US) structured and stored in the Tempus database. Demographics, clinical characteristics, molecular subtype, treatment history, and survival outcomes were assessed according to strict qualitative criteria. RNA sequencing and clinical data were used to predict molecular subtypes and signaling pathway enrichment.

RESULTS

The clinical abstraction cohort (n = 4000) mirrored the demographics and clinical characteristics of patients with breast cancer in the US, indicating feasibility for RWE generation. Among patients who were human epidermal growth factor receptor 2-positive (HER2⁺), 74.2% received anti-HER2 therapy, with ∼70% starting within 3 months of a positive test result. Most non-treated patients were early stage. In this RWD set, 31.7% of patients with HER2⁺ immunohistochemistry (IHC) had discordant fluorescence in situ hybridization results recorded. Among patients with multiple HER2 IHC results at diagnosis, 18.6% exhibited intra-test discordance. Through development of a whole-transcriptome model to predict IHC receptor status in the molecular sequenced cohort (n = 400), molecular subtypes were resolved for all patients (n = 36) with equivocal HER2 statuses from abstracted test results. Receptor-related signaling pathways were differentially enriched between clinical molecular subtypes.

CONCLUSIONS

RWD in the Tempus database mirrors the overall population of patients with breast cancer in the US. These results suggest that real-time, RWD analyses are feasible in a large, highly heterogeneous database. Furthermore, molecular data may aid deficiencies and discrepancies observed from breast cancer RWD.

Abstract 5474: Identification of novel druggable fusions enabled through the use of an automated RNA fusion prioritization pipeline

Gene fusions can serve as key drivers in the development of various cancers and represent important therapeutic targets and diagnostic biomarkers. Due to high detection of candidate fusions from RNA-sequencing data, there is a recognized need to build tools that will make reasonable and automated predictions to identify clinically or biologically relevant fusion events in a tumor sample. We developed a computational pipeline which scores and prioritizes all detected fusion transcripts within a sample to determine which fusions are likely driver events in the tumor. Specifically, the pipeline implements a categorization scheme that bins all scored fusion events into Low, Medium and High Confidence levels based on threshold read support levels and a DriverScore metric, which is derived from a binary classification algorithm using specific features, such as reading frame, breakpoint region, kinase domain and transcript isoform. We systematically analyzed 3200 fusion candidates from a previously published cohort of 500 paired tumor-normal samples sequenced with the Tempus xT assay. We found that 1.7% and 20.1% of fusion candidates were categorized in the High and Medium Confidence levels, respectively, while 78.2% of fusion events were deprioritized as Low Confidence calls. Of the 35 clinically-relevant fusions, 27 (77.1%) were captured in our prioritized set (High/Medium Confidence), including National Comprehensive Cancer Network actionable gene rearrangements involving RET, STAT6 and FUS, while the remaining 8 were assigned as Low Confidence due to an out of frame fusion transcript and insufficient read support. The frequency of prioritized fusions varied by cancer type, with prostate and breast cancer having the highest frequency of prioritized fusions. In addition to well-established canonical fusions, we also sought to characterize novel fusions, identifying a subset of 21 novel prioritized fusions which were also observed in The Cancer Genome Atlas tumor samples. Within this subset, 3% of fusion candidates contained a druggable domain such as a tyrosine kinase or Ras-binding domain, signifying the potential of categorization to enable novel fusion drug target discovery. Overall, our analysis highlights the utility of using an automated prioritization tool to detect known canonical fusion drivers and explore novel fusion drug targets and biomarkers.

Citation Format: Sumaiya A. Islam, Robert Huether, Emily Kudalkar. Identification of novel druggable fusions enabled through the use of an automated RNA fusion prioritization pipeline [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5474.

Abstract 3908: Universal genetic and transcriptomic concordance metrics to validate patient-derived tumor organoid models

Background

Patient derived tumor organoids (TOs) are emerging as potential models to elucidate mechanisms of tumor biology and therapeutic response. Here, we establish pan-cancer metrics for validation of genetic and transcriptomic recapitulation, and concordance of an organoid to its native tumor.

Methods/Results

We sequenced 50 tumor/TO pairs from 12 cancer types using the Tempus xT DNAseq panel and transcriptome RNAseq platforms. Concordance metrics between tumors and TOs were derived for genomic variants called by the DNA xT platform and comparative ratios were calculated for all detected somatic variants. Across all sequenced pairs, somatic variant detection concordance between any mutation identified in primary tissues and tumor organoids resulted in a mean value of 88.1%. Somatic primary tumor variant recapitulation, the percent of somatic variants identified in the primary tumors that were also detected in the TO, averaged 96.3%.

In addition to genetic concordance, DNAseq can identify and track clonal and subclonal diversity from source material to TO. In particular, we observed that >90% of source tumor/TO pairs harbor variants with allelic fractions <40% in both the sequenced TO and primary tumor tissue, suggesting intra-tumor heterogeneity in subclonal cell populations is maintained.

TOs and primary tumor transcriptomic profiles were compared by dimensionality reduction approaches (i.e. Uniform Manifold Approximation and Projection (UMAP), and Principal Components Analysis (PCA)) as well as differential expression analysis between cancer types. Overall, TOs recapitulated expected transcriptional programs of their tumor type as evidenced by UMAP and PCA as well as upregulation of defining pathways, such as estrogen receptor pathways in breast cancer TOs (ssGSEA p-values ranging from 0.004 to 5 × 10−5 for 5 gene ontology estrogen response pathways when compared to non-breast cancer TOs).

Conclusion

Determining genomic and transcriptomic concordance of TOs to source tumors is essential to confirm the validity of a given patient derived model. Our approach establishes metrics through key genomic features identified from routine next-generation sequencing data and can be extended beyond model validation to tracking clonal evolution over time in the presence or absence of therapeutic selection pressures. Our metrics may also serve as a critical quality control step if TOs are utilized in the clinical setting for personalized medicine.

Citation Format: Brandon L. Mapes, Joshua SK Bell, Lee F. Langer, Robert Huether, Catherine Igartua, Veronica Sanchez-Freire, Robert Tell, Jeffrey A. Borgia, Ashiq Masood, Ameen A. Salahudeen. Universal genetic and transcriptomic concordance metrics to validate patient-derived tumor organoid models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3908.

Damaging de novo missense variants in EEF1A2 lead to a developmental and degenerative epileptic-dyskinetic encephalopathy

Heterozygous de novo variants in the eukaryotic elongation factor EEF1A2 have previously been described in association with intellectual disability and epilepsy but never functionally validated. Here we report 14 new individuals with heterozygous EEF1A2 variants. We functionally validate multiple variants as protein-damaging using heterologous expression and complementation analysis. Our findings allow us to confirm multiple variants as pathogenic and broaden the phenotypic spectrum to include dystonia/choreoathetosis, and in some cases a degenerative course with cerebral and cerebellar atrophy. Pathogenic variants appear to act via a haploinsufficiency mechanism, disrupting both the protein synthesis and integrated stress response functions of EEF1A2. Our studies provide evidence that EEF1A2 is highly intolerant to variation and that de novo pathogenic variants lead to an epileptic-dyskinetic encephalopathy with both neurodevelopmental and neurodegenerative features. Developmental features may be driven by impaired synaptic protein synthesis during early brain development while progressive symptoms may be linked to an impaired ability to handle cytotoxic stressors.

Mutations in MAP3K1 that cause 46,XY disorders of sex development disrupt distinct structural domains in the protein

Missense mutations in the gene, MAP3K1, are a common cause of 46,XY gonadal dysgenesis, accounting for 15-20% of cases [Ostrer, 2014, Disorders of sex development (DSDs): an update. J. Clin. Endocrinol. Metab., 99, 1503-1509]. Functional studies demonstrated that all of these mutations cause a protein gain-of-function that alters co-factor binding and increases phosphorylation of the downstream MAP kinase pathway targets, MAPK11, MAP3K and MAPK1. This dysregulation of the MAP kinase pathway results in increased CTNNB1, increased expression of WNT4 and FOXL2 and decreased expression of SRY and SOX9. Unique and recurrent pathogenic mutations cluster in three semi-contiguous domains outside the kinase region of the protein, a newly identified N-terminal domain that shares homology with the Guanine Exchange Factor (residues Met164 to Glu231), a Plant HomeoDomain (residues Met442 to Trp495) and an ARMadillo repeat domain (residues Met566 to Glu862). Despite the presence of the mutation clusters and clinical data, there exists a dearth of mechanistic insights behind the development imbalance. In this paper, we use structural modeling and functional data of these mutations to understand alterations of the MAP3K1 protein and the effects on protein folding, binding and downstream target phosphorylation. We show that these mutations have differential effects on protein binding depending on the domains in which they occur. These mutations increase the binding of the RHOA, MAP3K4 and FRAT1 proteins and generally decrease the binding of RAC1. Thus, pathologies in MAP3K1 disrupt the balance between the pro-kinase activities of the RHOA and MAP3K4 binding partners and the inhibitory activity of RAC1.

Tumor Mutational Burden From Tumor-Only Sequencing Compared With Germline Subtraction From Paired Tumor and Normal Specimens

IMPORTANCE

Tumor mutation burden (TMB) is an emerging factor associated with survival with immunotherapy. When tumor-normal pairs are available, TMB is determined by calculating the difference between somatic and germline sequences. In the case of commonly used tumor-only sequencing, additional steps are needed to estimate the somatic alterations. Computational tools have been developed to determine germline contribution based on sample copy state, purity estimates, and occurrence of the variant in population databases; however, there is potential for sampling bias in population data sets.

OBJECTIVE

To investigate whether tumor-only filtering approaches overestimate TMB.

DESIGN, SETTING, AND PARTICIPANTS

This was a retrospective cohort study of 50 tumor samples from 10 different tumor types. A 595-gene panel test was used to assess TMB by adding all missense, indels, and frameshift variants with an allelic fraction of at least 5% and coverage of at least 100× within each tumor. Tumor-only TMB was evaluated against the criterion standard of matched germline-subtracted TMB at 3 levels. Level 1 removed all the tumor-only variants with allelic fraction of at least 1% in the Exome Aggregation Consortium database (with the Cancer Genome Atlas cohort removed). Level 2 removed all variants observed in population databases, simulating a naive approach of removing germline variation. Level 3 used an internal tumor-only pipeline for calculating TMB. These specimens were processed with a commercially available panel, and results were analyzed at the Mayo Clinic. Data were analyzed between December 1, 2018, and May 28, 2019.

MAIN OUTCOMES AND MEASURES

Tumor mutation burden per megabase (Mb) as determined by 3 levels of filtering and germline subtraction.

RESULTS

There were significantly higher estimates of TMB with level 1 (median [range] mutations per Mb, 28.8 [17.5-67.1]), level 2 (median [range] mutations per Mb, 20.8 [10.4-30.8]), and level 3 (median [range] mutations per Mb, 3.8 [0.8-12.1]) tumor-only filtering approaches than those determined by germline subtraction (median [range] mutations per Mb, 1.7 [0.4-9.2]). There were no strong associations between TMB estimates and tumor-germline TMB for level 1 filtering (r = 0.008; 95% CI, -0.004 to 0.020), level 2 filtering (r = 0.018; 95% CI, 0.003 to 0.033), or level 3 filtering (r = 0.54; 95% CI, 0.36 to 0.68).

CONCLUSIONS AND RELEVANCE

The findings of this study indicate that tumor-only approaches that filter variants in population databases can overestimate TMB compared with germline subtraction methods. Despite improved association with more stringent filtering approaches, these falsely elevated estimates may result in the inappropriate categorization of tumor specimens and negatively affect clinical trial results and patient outcomes.

Gene-specific criteria for PTEN variant curation: Recommendations from the ClinGen PTEN Expert Panel

The ClinGen PTEN Expert Panel was organized by the ClinGen Hereditary Cancer Clinical Domain Working Group to assemble clinicians, researchers, and molecular diagnosticians with PTEN expertise to develop specifications to the 2015 ACMG/AMP Sequence Variant Interpretation Guidelines for PTEN variant interpretation. We describe finalized PTEN-specific variant classification criteria and outcomes from pilot testing of 42 variants with benign/likely benign (BEN/LBEN), pathogenic/likely pathogenic (PATH/LPATH), uncertain significance (VUS), and conflicting (CONF) ClinVar assertions. Utilizing these rules, classifications concordant with ClinVar assertions were achieved for 14/15 (93.3%) BEN/LBEN and 16/16 (100%) PATH/LPATH ClinVar consensus variants for an overall concordance of 96.8% (30/31). The variant where agreement was not reached was a synonymous variant near a splice donor with noncanonical sequence for which in silico models cannot predict the native site. Applying these rules to six VUS and five CONF variants, adding shared internal laboratory data enabled one VUS to be classified as LBEN and two CONF variants to be as classified as PATH and LPATH. This study highlights the benefit of gene-specific criteria and the value of sharing internal laboratory data for variant interpretation. Our PTEN-specific criteria and expertly reviewed assertions should prove helpful for laboratories and others curating PTEN variants.

Overestimation of tumor mutational burden (TMB) using algorithms compared to germline subtraction

2621

Background: TMB is an emerging predictor of survival with immunotherapy. TMB is determined by taking the difference between somatic and germline datasets when tumor-normal pairs are available. In the case of commonly utilized tumor-only sequencing, additional steps are needed to estimate the somatic alterations. Computational tools have been developed that determine germline contribution based on sample copy state, purity estimates and occurrence of the variant in population databases. Given the potential bias of population datasets, we hypothesized that tumor-only filtering approaches may overestimate the actual TMB. Methods: We assessed the TMB from 50 tumors in 10 diseases including all missense, indels, and frameshift variants with an allelic fraction (AF) ≥5% and Coverage ≥100X within the tumor. Tumor-only TMB was evaluated against the gold standard of matched germline subtracted TMB at three levels. Level 1 removed all the tumor-only variants with AF in the non-TCGA ExAC database ≥1%. Level 2 removed all variants observed in population databases simulating a naive approach of removing germline variation. Level 3 used an internal tumor-only pipeline for calculating TMB. Results: There were significantly higher estimates of TMB with Level 1, Level 2 and Level 3 tumor-only filtering approaches than that determined by germline subtraction, resulting in significant bias. Whereas there was no correlation between TMB estimates and tumor-germline TMB for Level 1 filtering, there were improvements in correlations for Level 2 and Level 3. Conclusions: The tumor-only approaches that filter variants in population databases overestimate TMB compared to that determined by germline subtraction. Despite improved correlations with more stringent filtering approaches, these falsely elevated estimates may result in the inappropriate categorization of tumor specimens and negatively impact clinical trial results and patient outcomes. [Table: see text]

Clinical validation of the tempus xT next-generation targeted oncology sequencing assay

We developed and clinically validated a hybrid capture next generation sequencing assay to detect somatic alterations and microsatellite instability in solid tumors and hematologic malignancies. This targeted oncology assay utilizes tumor-normal matched samples for highly accurate somatic alteration calling and whole transcriptome RNA sequencing for unbiased identification of gene fusion events. The assay was validated with a combination of clinical specimens and cell lines, and recorded a sensitivity of 99.1% for single nucleotide variants, 98.1% for indels, 99.9% for gene rearrangements, 98.4% for copy number variations, and 99.9% for microsatellite instability detection. This assay presents a wide array of data for clinical management and clinical trial enrollment while conserving limited tissue.

A multi-institutional study assessing prevalence of deleterious germline mutations in pancreatic cancer

280

Background: Pancreatic cancer is being increasingly associated with germline implications. Some large single-center studies have reported results ranging from 3.9% to 19.8% of patients found to have germline variants [Shindo, JCO 2017; Lowery, JNCI 2018]. Due to this wide range, we aim to further delineate prevalence of deleterious germline mutations in pancreatic cancer using a multi-institutional data set. We also aim to analyze predictive factors such as mutant allele frequency (MAF, in %) in germline versus somatic calls. Methods: We sequenced 23 genes in DNA prepared from clinical tissue and blood specimens submitted to Tempus Labs. Germline variants and somatic variants were processed separately. Germline variants were determined to be deleterious through the sum effect of a combination of in silico predictors, population databases, and internal evaluations. Tumor-normal comparisons were used to define somatic versus germline, and MAFs were calculated for each. Results: A total of 234 patient samples from 17 institutions were analyzed. Of these, 12 (5.1%) had predicted deleterious germline variants involving 8 different genes: BRCA1 (n = 3), CHEK2 (n = 3), ATM (n = 1), MLH1 (n = 1), MUTYH (n = 1), PALB2 (n = 1), SMAD4 (n = 1), TP53 (n = 1). For most somatic alterations, the MAFs were found to be greater than the germline deleterious alterations, with the latter approaching ~50% in most cases (Table). Conclusions: This multi-institutional study identifies 5% of patients with pancreatic cancer to have deleterious germline alterations. Somatic variant testing, particularly when paired with germline, can be used as a screening method for genetic counseling referrals, especially with MAF analyses of paired tumor-normal samples. [Table: see text]

Association of Breast and Ovarian Cancers With Predisposition Genes Identified by Large-Scale Sequencing

Importance

Since the discovery of BRCA1 and BRCA2, multiple high- and moderate-penetrance genes have been reported as risk factors for hereditary breast cancer, ovarian cancer, or both; however, it is unclear whether these findings represent the complete genetic landscape of these cancers. Systematic investigation of the genetic contributions to breast and ovarian cancers is needed to confirm these findings and explore potentially new associations.

Objective

To confirm reported and identify additional predisposition genes for breast or ovarian cancer.

Design, Setting, and Participants

In this sample of 11 416 patients with clinical features of breast cancer, ovarian cancer, or both who were referred for genetic testing from 1200 hospitals and clinics across the United States and of 3988 controls who were referred for genetic testing for noncancer conditions between 2014 and 2015, whole-exome sequencing was conducted and gene-phenotype associations were examined. Case-control analyses using the Genome Aggregation Database as a set of reference controls were also conducted.

Main Outcomes and Measures

Breast cancer risk associated with pathogenic variants among 625 cancer predisposition genes; association of identified predisposition breast or ovarian cancer genes with the breast cancer subtypes invasive ductal, invasive lobular, hormone receptor-positive, hormone receptor-negative, and male, and with early-onset disease.

Results

Of 9639 patients with breast cancer, 3960 (41.1%) were early-onset cases (≤45 years at diagnosis) and 123 (1.3%) were male, with men having an older age at diagnosis than women (mean [SD] age, 61.8 [12.8] vs 48.6 [11.4] years). Of 2051 women with ovarian cancer, 445 (21.7%) received a diagnosis at 45 years or younger. Enrichment of pathogenic variants were identified in 4 non-BRCA genes associated with breast cancer risk: ATM (odds ratio [OR], 2.97; 95% CI, 1.67-5.68), CHEK2 (OR, 2.19; 95% CI, 1.40-3.56), PALB2 (OR, 5.53; 95% CI, 2.24-17.65), and MSH6 (OR, 2.59; 95% CI, 1.35-5.44). Increased risk for ovarian cancer was associated with 4 genes: MSH6 (OR, 4.16; 95% CI, 1.95-9.47), RAD51C (OR, not estimable; false-discovery rate-corrected P = .004), TP53 (OR, 18.50; 95% CI, 2.56-808.10), and ATM (OR, 2.85; 95% CI, 1.30-6.32). Neither the MRN complex genes nor CDKN2A was associated with increased breast or ovarian cancer risk. The findings also do not support previously reported breast cancer associations with the ovarian cancer susceptibility genes BRIP1, RAD51C, and RAD51D, or mismatch repair genes MSH2 and PMS2.

Conclusions and Relevance

The results of this large-scale exome sequencing of patients and controls shed light on both well-established and controversial non-BRCA predisposition gene associations with breast or ovarian cancer reported to date and may implicate additional breast or ovarian cancer susceptibility gene candidates involved in DNA repair and genomic maintenance.

Clinical validation of the Tempus xO assay

We have developed a clinically validated NGS assay that includes tumor, germline and RNA sequencing. We apply this assay to clinical specimens and cell lines, and we demonstrate a clinical sensitivity of 98.4% and positive predictive value of 100% for the clinically actionable variants measured by the assay. We also demonstrate highly accurate copy number measurements and gene rearrangement identification.

Associations Between Cancer Predisposition Testing Panel Genes and Breast Cancer

IMPORTANCE

Germline pathogenic variants in BRCA1 and BRCA2 predispose to an increased lifetime risk of breast cancer. However, the relevance of germline variants in other genes from multigene hereditary cancer testing panels is not well defined.

OBJECTIVE

To determine the risks of breast cancer associated with germline variants in cancer predisposition genes.

DESIGN, SETTING, AND PARTICIPANTS

A study population of 65 057 patients with breast cancer receiving germline genetic testing of cancer predisposition genes with hereditary cancer multigene panels. Associations between pathogenic variants in non-BRCA1 and non-BRCA2 predisposition genes and breast cancer risk were estimated in a case-control analysis of patients with breast cancer and Exome Aggregation Consortium reference controls. The women underwent testing between March 15, 2012, and June 30, 2016.

MAIN OUTCOMES AND MEASURES

Breast cancer risk conferred by pathogenic variants in non-BRCA1 and non-BRCA2 predisposition genes.

RESULTS

The mean (SD) age at diagnosis for the 65 057 women included in the analysis was 48.5 (11.1) years. The frequency of pathogenic variants in 21 panel genes identified in 41 611 consecutively tested white women with breast cancer was estimated at 10.2%. After exclusion of BRCA1, BRCA2, and syndromic breast cancer genes (CDH1, PTEN, and TP53), observed pathogenic variants in 5 of 16 genes were associated with high or moderately increased risks of breast cancer: ATM (OR, 2.78; 95% CI, 2.22-3.62), BARD1 (OR, 2.16; 95% CI, 1.31-3.63), CHEK2 (OR, 1.48; 95% CI, 1.31-1.67), PALB2 (OR, 7.46; 95% CI, 5.12-11.19), and RAD51D (OR, 3.07; 95% CI, 1.21-7.88). Conversely, variants in the BRIP1 and RAD51C ovarian cancer risk genes; the MRE11A, RAD50, and NBN MRN complex genes; the MLH1 and PMS2 mismatch repair genes; and NF1 were not associated with increased risks of breast cancer.

CONCLUSIONS AND RELEVANCE

This study establishes several panel genes as high- and moderate-risk breast cancer genes and provides estimates of breast cancer risk associated with pathogenic variants in these genes among individuals qualifying for clinical genetic testing.

DNM1 encephalopathy: A new disease of vesicle fission

OBJECTIVE

To evaluate the phenotypic spectrum caused by mutations in dynamin 1 (DNM1), encoding the presynaptic protein DNM1, and to investigate possible genotype-phenotype correlations and predicted functional consequences based on structural modeling.

METHODS

We reviewed phenotypic data of 21 patients (7 previously published) with DNM1 mutations. We compared mutation data to known functional data and undertook biomolecular modeling to assess the effect of the mutations on protein function.

RESULTS

We identified 19 patients with de novo mutations in DNM1 and a sibling pair who had an inherited mutation from a mosaic parent. Seven patients (33.3%) carried the recurrent p.Arg237Trp mutation. A common phenotype emerged that included severe to profound intellectual disability and muscular hypotonia in all patients and an epilepsy characterized by infantile spasms in 16 of 21 patients, frequently evolving into Lennox-Gastaut syndrome. Two patients had profound global developmental delay without seizures. In addition, we describe a single patient with normal development before the onset of a catastrophic epilepsy, consistent with febrile infection-related epilepsy syndrome at 4 years. All mutations cluster within the GTPase or middle domains, and structural modeling and existing functional data suggest a dominant-negative effect on DMN1 function.

CONCLUSIONS

The phenotypic spectrum of DNM1-related encephalopathy is relatively homogeneous, in contrast to many other genetic epilepsies. Up to one-third of patients carry the recurrent p.Arg237Trp variant, which is now one of the most common recurrent variants in epileptic encephalopathies identified to date. Given the predicted dominant-negative mechanism of this mutation, this variant presents a prime target for therapeutic intervention.

Abstract S2-01: Breast cancer risks associated with mutations in cancer predisposition genes identified by clinical genetic testing of 60,000 breast cancer patients

Clinical genetic testing panels are broadly used to gather information about cancer predisposition in individuals with personal and/or family history of breast cancer. However, the involvement of several of the genes on clinical testing panels in predisposition to breast cancer, such as MRE11A and RAD50, has recently come into question. In addition, accurate risk estimates for breast and other cancer are not well defined for the majority of genes on testing panels. We studied 60,000 women diagnosed with breast cancer who were tested for germline cancer predisposing mutations using hereditary cancer gene panels. Information on personal and family cancer history, age of diagnosis, and ethnicity of patients was obtained from test requisition forms. Greater than 90% met National Comprehensive Cancer Network HBOC testing criteria. To estimate gene-specific risks for breast cancer, case-control analyses were performed comparing the frequencies of pathogenic mutations from Caucasian cancer cases with frequencies from Caucasian, non-Finnish, non-TCGA controls from the Exome Aggregation Consortium (ExAC) database. Mutations were detected in 9% of breast cancer patients. Twelve genes displayed a significant association (p<0.05) with breast cancer. Nine of these genes, including ATM, RAD51D, NF1, and MSH6, were associated with moderate risk (RR>2.0) of breast cancer and three genes (BRCA1, BRCA2, PALB2) were associated with high risk (RR>5.0) of breast cancer. Cumulative age-dependent risk models were developed for each gene. This large clinical testing dataset of 60,000 women with breast cancer provides useful data for many predisposition genes previously lacking risk estimates, and should prove useful for clinical risk management of patients with inherited mutations in these genes.

Citation Format: Couch FJ, Hu C, Lilyquist J, Shimelis H, Akinhanmi M, Na J, Polley EC, Hart SN, McFarland R, LaDuca H, Huether R, Goldgar DE, Dolinsky JS. Breast cancer risks associated with mutations in cancer predisposition genes identified by clinical genetic testing of 60,000 breast cancer patients [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr S2-01.

Beyond DNA: An Integrated and Functional Approach for Classifying Germline Variants in Breast Cancer Genes

Genetic testing for hereditary breast cancer is an integral part of individualized care in the new era of precision medicine. The accuracy of an assay is reliant on not only the technology and bioinformatics analysis utilized but also the experience and infrastructure required to correctly classify genetic variants as disease-causing. Interpreting the clinical significance of germline variants identified by hereditary cancer testing is complex and has a significant impact on the management of patients who are at increased cancer risk. In this review we give an overview of our clinical laboratory's integrated approach to variant assessment. We discuss some of the nuances that should be considered in the assessment of genomic variants. In addition, we highlight lines of evidence such as functional assays and structural analysis that can be useful in the assessment of rare and complex variants.

Further evidence that de novo missense and truncating variants in ZBTB18 cause intellectual disability with variable features

Identification of rare genetic variants in patients with intellectual disability (ID) has been greatly accelerated by advances in next generation sequencing technologies. However, due to small numbers of patients, the complete phenotypic spectrum associated with pathogenic variants in single genes is still emerging. Among these genes is ZBTB18 (ZNF238), which is deleted in patients with 1q43q44 microdeletions who typically present with ID, microcephaly, corpus callosum (CC) abnormalities, and seizures. Here we provide additional evidence for haploinsufficiency or dysfunction of the ZBTB18 gene as the cause of ID in five unrelated patients with variable syndromic features who underwent whole exome sequencing revealing separate de novo pathogenic or likely pathogenic variants in ZBTB18 (two missense alterations and three truncating alterations). The neuroimaging findings in our cohort (CC hypoplasia seen in 4/4 of our patients who underwent MRI) lend further support for ZBTB18 as a critical gene for CC abnormalities. A similar phenotype of microcephaly, CC agenesis, and cerebellar vermis hypoplasia has been reported in mice with central nervous system-specific knockout of Zbtb18. Our five patients, in addition to the previously described cases of de novo ZBTB18 variants, add to knowledge about the phenotypic spectrum associated with ZBTB18 haploinsufficiency/dysfunction.

A recurrent mutation in KCNA2 as a novel cause of hereditary spastic paraplegia and ataxia

The hereditary spastic paraplegias (HSPs) are heterogeneous neurodegenerative disorders with over 50 known causative genes. We identified a recurrent mutation in KCNA2 (c.881G>A, p.R294H), encoding the voltage-gated K(+) -channel, KV 1.2, in two unrelated families with HSP, intellectual disability (ID), and ataxia. Follow-up analysis of > 2,000 patients with various neurological phenotypes identified a de novo p.R294H mutation in a proband with ataxia and ID. Two-electrode voltage-clamp recordings of Xenopus laevis oocytes expressing mutant KV 1.2 channels showed loss of function with a dominant-negative effect. Our findings highlight the phenotypic spectrum of a recurrent KCNA2 mutation, implicating ion channel dysfunction as a novel HSP disease mechanism. Ann Neurol 2016.

Candidate-gene criteria for clinical reporting: diagnostic exome sequencing identifies altered candidate genes among 8% of patients with undiagnosed diseases

Purpose:

Diagnostic exome sequencing (DES) is now a commonly ordered test for individuals with undiagnosed genetic disorders. In addition to providing a diagnosis for characterized diseases, exome sequencing has the capacity to uncover novel candidate genes for disease.

Methods:

Family-based DES included analysis of both characterized and novel genetic etiologies. To evaluate candidate genes for disease in the clinical setting, we developed a systematic, rule-based classification schema.

Results:

Testing identified a candidate gene among 7.7% (72/934) of patients referred for DES; 37 (4.0%) and 35 (3.7%) of the genes received evidence scores of “candidate” and “suspected candidate,” respectively. A total of 71 independent candidate genes were reported among the 72 patients, and 38% (27/71) were subsequently corroborated in the peer-reviewed literature. This rate of corroboration increased to 51.9% (27/52) among patients whose gene was reported at least 12 months previously.

Conclusions:

Herein, we provide transparent, comprehensive, and standardized scoring criteria for the clinical reporting of candidate genes. These results demonstrate that DES is an integral tool for genetic diagnosis, especially for elucidating the molecular basis for both characterized and novel candidate genetic etiologies. Gene discoveries also advance the understanding of normal human biology and more common diseases.

Genet Med19 2, 224–235.

Abstract 2597: Breast and ovarian cancer risks associated with cancer predisposition gene mutations identified by multigene panel testing

Multigene panel testing (MGPT) for hereditary cancer is increasing in popularity in the USA. Many panels include genes identified as hereditary breast and/or ovarian cancer (HBOC) genes despite limited data regarding the precise cancer risks associated with mutations in these genes. Here we report on results from BreastNext and OvaNext panel testing of 20 genes (ATM, BARD1, BRCA1, BRCA2, BRIP1, CDH1, CHEK2, MLH1, MRE11A, MSH2, MSH6, NBN, NF1, PALB2, PMS2, PTEN, RAD50, RAD51C, RAD51D, TP53) in a cohort of 15,083 individuals. The majority of individuals were from high-risk breast and/or ovarian (Br/Ov) cancer families, with 92.4% of all probands meeting National Comprehensive Cancer Network HBOC testing criteria. Pathogenic mutations were identified in 9.4% of the overall cohort.

To estimate gene-specific breast and ovarian cancer risks, case-control analyses were performed comparing the frequencies of pathogenic mutations from Caucasian breast or ovarian cancer cases from BreastNext and OvaNext with frequencies from Caucasian, non-Finnish, non-TCGA controls from the Exome Aggregation Consortium (ExAC) database. Mutations in the well studied ATM and CHEK2 genes were associated with moderate risks (OR>2) of breast cancer and mutations in PALB2 were associated with high-risks (OR>5) of breast cancer, consistent with previous reports. In addition, the study suggested that pathogenic mutations in MSH6, RAD51D, CDH1, and NF1 are associated with moderate to high risks of breast cancer. In contrast, RAD51C, RAD51D, and BRIP1 mutations were associated with high risks of ovarian cancer, PALB2 mutations were associated with moderate risks, but ATM and CHEK2 mutations were not associated with increased ovarian cancer risk. In addition, modeling of missense mutations in the predisposition genes using in silico prediction algorithms suggested that missense mutations in CDH1, CHEK2, MSH2, and MSH6 are associated with moderate risks of breast cancer and missense mutations in RAD51C increase risks of ovarian cancer. This large breast and ovarian cancer case-control analysis provides useful data for many predisposition genes previously lacking risk estimates, and should prove useful for clinical risk management of patients after clinical panel testing.

Citation Format: Fergus J. Couch, David E. Goldgar, Steven N. Hart, Emily Hallberg, Raymond Moore, Huong Meeks, Robert Huether, Holly LaDuca, Elizabeth Chao, Jill Dolinsky. Breast and ovarian cancer risks associated with cancer predisposition gene mutations identified by multigene panel testing. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2597.

Germline activating MTOR mutation arising through gonadal mosaicism in two brothers with megalencephaly and neurodevelopmental abnormalities

Background

In humans, Mammalian Target of Rapamycin (MTOR) encodes a 300 kDa serine/ threonine protein kinase that is ubiquitously expressed, particularly at high levels in brain. MTOR functions as an integrator of multiple cellular processes, and in so doing either directly or indirectly regulates the phosphorylation of at least 800 proteins. While somatic MTOR mutations have been recognized in tumors for many years, and more recently in hemimegalencephaly, germline MTOR mutations have rarely been described.

Case presentation

We report the successful application of family-trio Diagnostic Exome Sequencing (DES) to identify the underlying molecular etiology in two brothers with multiple neurological and developmental lesions, and for whom previous testing was non-diagnostic. The affected brothers, who were 6 and 23 years of age at the time of DES, presented symptoms including but not limited to mild Autism Spectrum Disorder (ASD), megalencephaly, gross motor skill delay, cryptorchidism and bilateral iris coloboma. Importantly, we determined that each affected brother harbored the MTOR missense alteration p.E1799K (c.5395G>A). This exact variant has been previously identified in multiple independent human somatic cancer samples and has been shown to result in increased MTOR activation. Further, recent independent reports describe two unrelated families in whom p.E1799K co-segregated with megalencephaly and intellectual disability (ID); in both cases, p.E1799K was shown to have originated due to germline mosaicism. In the case of the family reported herein, the absence of p.E1799K in genomic DNA extracted from the blood of either parent suggests that this alteration most likely arose due to gonadal mosaicism. Further, the p.E1799K variant exerts its effect by a gain-of-function (GOF), autosomal dominant mechanism.

Conclusion

Herein, we describe the use of DES to uncover an activating MTOR missense alteration of gonadal mosaic origin that is likely to be the causative mutation in two brothers who present multiple neurological and developmental abnormalities. Our report brings the total number of families who harbor MTOR p.E1799K in association with megalencephaly and ID to three. In each case, evidence suggests that p.E1799K arose in the affected individuals due to gonadal mosaicism. Thus, MTOR p.E1799K can now be classified as a pathogenic GOF mutation that causes megalencephaly and cognitive impairment in humans.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0240-8) contains supplementary material, which is available to authorized users.

Mutations in RASA1 and GDF2 identified in patients with clinical features of hereditary hemorrhagic telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant vascular disorder caused by mutations in ENG, ACVRL1 and SMAD4, which function in regulating the transforming growth factor beta and bone morphogenetic protein signaling pathways. Symptoms of HHT can be present in individuals who test negative for mutations in these three genes indicating other genes may be involved. In this study, we tested for mutations in two genes, RASA1 and GDF2, which were recently reported to be involved in vascular disorders. To determine whether RASA1 and GDF2 have phenotypic overlap with HHT and should be included in diagnostic testing, we developed a next-generation sequencing assay to detect mutations in 93 unrelated individuals who previously tested negative for mutations in ENG, ACVRL1 and SMAD4, but were clinically suspected to have HHT. Pathogenic mutations in RASA1 were identified in two samples (2.15%) and a variant of unknown significance in GDF2 was detected in one sample. All three individuals experienced epistaxis with dermal lesions described in medical records as telangiectases. These results indicate that the inclusion of RASA1 and GDF2 screening in individuals suspected to have HHT will increase the detection rate and aid clinicians in making an accurate diagnosis.

The landscape of somatic mutations in infant MLL-rearranged acute lymphoblastic leukemias

Infant acute lymphoblastic leukemia (ALL) with MLL rearrangements (MLL-R) represents a distinct leukemia with a poor prognosis. To define its mutational landscape, we performed whole genome, exome, RNA and targeted DNA sequencing on 65 infants (47 MLL-R and 18 non-MLL-R) and 20 older children (MLL-R cases) with leukemia. Our data demonstrated infant MLL-R ALL to have one of the lowest frequencies of somatic mutations of any sequenced cancer, with the predominant leukemic clone carrying a mean of 1.3 non-silent mutations. Despite the paucity of mutations, activating mutations in kinase/PI3K/RAS signaling pathways were detected in 47%. Surprisingly, however, these mutations were often sub-clonal and frequently lost at relapse. In contrast to infant cases, MLL-R leukemia in older children had more somatic mutations (a mean of 6.5/case versus 1.3/case, P=7.15×10⁻⁵) and contained frequent mutations (45%) in epigenetic regulators, a category of genes that with the exception of MLL was rarely mutated in infant MLL-R ALL.

Survival analysis of infected mice reveals pathogenic variations in the genome of avian H1N1 viruses

Most influenza pandemics have been caused by H1N1 viruses of purely or partially avian origin. Here, using Cox proportional hazard model, we attempt to identify the genetic variations in the whole genome of wild-type North American avian H1N1 influenza A viruses that are associated with their virulence in mice by residue variations, host origins of virus (Anseriformes-ducks or Charadriiformes-shorebirds), and host-residue interactions. In addition, through structural modeling, we predicted that several polymorphic sites associated with pathogenicity were located in structurally important sites, especially in the polymerase complex and NS genes. Our study introduces a new approach to identify pathogenic variations in wild-type viruses circulating in the natural reservoirs and ultimately to understand their infectious risks to humans as part of risk assessment efforts towards the emergence of future pandemic strains.

Abstract PR03: The genomic landscape of diffuse intrinsic pontine glioma and pediatric non-brainstem high-grade glioma

Pediatric high-grade glioma (HGG) remains a tremendous clinical challenge, with a two-year survival of less than 20%. We analyzed 127 pediatric HGGs, including diffuse intrinsic pontine gliomas (DIPGs) and non-brainstem HGGs (NBS-HGGs) by whole-genome, whole-exome, and/or transcriptome sequencing. Somatic mutations in the bone morphogenetic protein (BMP) receptor ACVR1 occurred in 32% of DIPG, a finding exclusive to brainstem HGG. Structural variants generating fusion genes were found in 47% of pediatric HGG, with recurrent fusions involving the neurotrophin receptor genes NTRK1, 2, or 3 in 40% of infant NBS-HGGs and 5% of pediatric HGG overall. Multiple mutations targeted pathways involving histone modification or chromatin remodeling, cell cycle regulation and receptor tyrosine kinase/RAS/PI3K signaling, in both DIPG and NBS-HGGs at frequencies of greater than 39% in the entire cohort. The HGG mutation burden ranged from 2 non-silent mutations in an infant HGG to more than a million mutations in a tumor associated with germline mismatch repair deficiency. From these findings, we have established novel tumor models to better understand this devastating disease. This work provides new insight into the genetic events driving pediatric HGG tumorigenesis.

This abstract is also presented as Poster B14.

Citation Format: Alexander K. Diaz, Gang Wu, Barbara S. Paugh, Yongjin Li, Xiaoyan Zhu, Sherri Rankin, Chunxu Qu, Xiang Chen, Junyuan Zhang, John Easton, Michael Edmonson, Charles Lu, Panduka Nagahawatte, Erin Hedlund, Michael Rusch, Stanley Pounds, Tong Lin, Arzu Onar-Thomas, Robert Huether, Richard Kriwacki, Matthew Parker, Pankaj Gupta, Jared Becksfort, Lei Wei, Heather L. Mulder, Kristy Boggs, Bhavin Vadodaria, Donald Yergeau, Kerri Ochoa, Robert S. Fulton, Lucinda S. Fulton, Chris Jones, Alberto Broniscer, Cynthia Wetmore, Amar Gajjar, Li Ding, Elaine R. Mardis, Richard K. Wilson, James R. Downing, David W. Ellison, Jinghui Zhang, Suzanne J. Baker, For the St Jude Children's Research Hospital – Washington University Pediatric Cancer Genome Project. The genomic landscape of diffuse intrinsic pontine glioma and pediatric non-brainstem high-grade glioma. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr PR03.

Abstract 2930: Global chromatin profiling reveals NSD2 mutation in pediatric ALL

Epigenetic dysregulation is an emerging hallmark of cancers. We developed a high-information-content mass spectrometry approach to profile global histone modifications in human cancers. When applied to 115 lines of the Cancer Cell Line Encyclopedia1, this approach identified distinct molecular chromatin signatures. One signature was characterized by increased H3K36 dimethylation, exhibited by several lines harboring NSD2 translocations. A novel NSD2 p.E1099K variant was identified in non-translocated acute lymphoblastic leukemia (ALL) lines sharing this signature. Ectopic expression of the variant induced a chromatin signature characteristic of NSD2 hyperactivation and promoted transformation. NSD2 knockdown selectively inhibited the proliferation of NSD2-mutant lines and impaired the in vivo growth of an NSD2-mutant ALL xenograft. Sequencing analysis of >1000 pediatric cancer genomes identified the NSD2 p.E1099K mutation in 14% of t(12;21)[ETV6-RUNX1]-containing ALLs. These findings identify NSD2 as a potential therapeutic target for pediatric ALL and provide a general framework for the functional annotation of cancer epigenomes.

1.

Barretina,J. et al. The Cancer Cell Line Encyclopedia enables predictive modelling of anticancer drug sensitivity. Nature 483, 603-607 (2012).

Citation Format: Ho Man Chan, Jacob D. Jaffe, Yan Wang, Jinghui Zhang, Robert Huether, Gregory V. Kryukov, Hyo-eun C. Bhang, Jordan E. Taylor, Min Hu, Nathan P. Englund, Feng Yan, Zhaofu Wang, E Robert McDonald III, Lei Wei, Jing Ma, John Easton, Zhengtian Yu, Rosalie deBeaumount, Veronica Gibaja, Kavitha Venkatesan, Robert Schlegel, William R. Sellers, Nicholas Keen, Jun Liu, Giordano Caponigro, Jordi Barretina, Vesselina G. Cooke, Charles Mullighan, Steven A. Carr, James R. Downing, Levi A. Garraway, Frank Stegmeier. Global chromatin profiling reveals NSD2 mutation in pediatric ALL. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2930. doi:10.1158/1538-7445.AM2014-2930

The landscape of somatic mutations in epigenetic regulators across 1,000 paediatric cancer genomes

Studies of paediatric cancers have shown a high frequency of mutation across epigenetic regulators. Here we sequence 633 genes, encoding the majority of known epigenetic regulatory proteins, in over 1,000 paediatric tumours to define the landscape of somatic mutations in epigenetic regulators in paediatric cancer. Our results demonstrate a marked variation in the frequency of gene mutations across 21 different paediatric cancer subtypes, with the highest frequency of mutations detected in high-grade gliomas, T-lineage acute lymphoblastic leukaemia and medulloblastoma, and a paucity of mutations in low-grade glioma and retinoblastoma. The most frequently mutated genes are H3F3A, PHF6, ATRX, KDM6A, SMARCA4, ASXL2, CREBBP, EZH2, MLL2, USP7, ASXL1, NSD2, SETD2, SMC1A and ZMYM3. We identify novel loss-of-function mutations in the ubiquitin-specific processing protease 7 (USP7) in paediatric leukaemia, which result in decreased deubiquitination activity. Collectively, our results help to define the landscape of mutations in epigenetic regulatory genes in paediatric cancer and yield a valuable new database for investigating the role of epigenetic dysregulations in cancer.

The genomic landscape of diffuse intrinsic pontine glioma and pediatric non-brainstem high-grade glioma

Pediatric high-grade glioma (HGG) is a devastating disease with a two-year survival of less than 20%¹. We analyzed 127 pediatric HGGs, including diffuse intrinsic pontine gliomas (DIPGs) and non-brainstem HGGs (NBS-HGGs) by whole genome, whole exome, and/or transcriptome sequencing. We identified recurrent somatic mutations in ACVR1 exclusively in DIPG (32%), in addition to the previously reported frequent somatic mutations in histone H3, TP53 and ATRX in both DIPG and NBS-HGGs^2-5. Structural variants generating fusion genes were found in 47% of DIPGs and NBS-HGGs, with recurrent fusions involving the neurotrophin receptor genes NTRK1, 2, or 3 in 40% of NBS-HGGs in infants. Mutations targeting receptor tyrosine kinase/RAS/PI3K signaling, histone modification or chromatin remodeling, and cell cycle regulation were found in 68%, 73% and 59%, respectively, of pediatric HGGs, including DIPGs and NBS-HGGs. This comprehensive analysis provides insights into the unique and shared pathways driving pediatric HGG within and outside the brainstem.

Whole-genome sequencing identifies genetic alterations in pediatric low-grade gliomas

The most common pediatric brain tumors are low-grade gliomas (LGGs). We used whole-genome sequencing to identify multiple new genetic alterations involving BRAF, RAF1, FGFR1, MYB, MYBL1 and genes with histone-related functions, including H3F3A and ATRX, in 39 LGGs and low-grade glioneuronal tumors (LGGNTs). Only a single non-silent somatic alteration was detected in 24 of 39 (62%) tumors. Intragenic duplications of the portion of FGFR1 encoding the tyrosine kinase domain (TKD) and rearrangements of MYB were recurrent and mutually exclusive in 53% of grade II diffuse LGGs. Transplantation of Trp53-null neonatal astrocytes expressing FGFR1 with the duplication involving the TKD into the brains of nude mice generated high-grade astrocytomas with short latency and 100% penetrance. FGFR1 with the duplication induced FGFR1 autophosphorylation and upregulation of the MAPK/ERK and PI3K pathways, which could be blocked by specific inhibitors. Focusing on the therapeutically challenging diffuse LGGs, our study of 151 tumors has discovered genetic alterations and potential therapeutic targets across the entire range of pediatric LGGs and LGGNTs.

The genomic landscape of hypodiploid acute lymphoblastic leukemia

The genetic basis of hypodiploid acute lymphoblastic leukemia (ALL), a subtype of ALL characterized by aneuploidy and poor outcome, is unknown. Genomic profiling of 124 hypodiploid ALL cases, including whole-genome and exome sequencing of 40 cases, identified two subtypes that differ in the severity of aneuploidy, transcriptional profiles and submicroscopic genetic alterations. Near-haploid ALL with 24-31 chromosomes harbor alterations targeting receptor tyrosine kinase signaling and Ras signaling (71%) and the lymphoid transcription factor gene IKZF3 (encoding AIOLOS; 13%). In contrast, low-hypodiploid ALL with 32-39 chromosomes are characterized by alterations in TP53 (91.2%) that are commonly present in nontumor cells, IKZF2 (encoding HELIOS; 53%) and RB1 (41%). Both near-haploid and low-hypodiploid leukemic cells show activation of Ras-signaling and phosphoinositide 3-kinase (PI3K)-signaling pathways and are sensitive to PI3K inhibitors, indicating that these drugs should be explored as a new therapeutic strategy for this aggressive form of leukemia.

Novel mutations target distinct subgroups of medulloblastoma

Medulloblastoma is a malignant childhood brain tumour comprising four discrete subgroups. Here, to identify mutations that drive medulloblastoma, we sequenced the entire genomes of 37 tumours and matched normal blood. One-hundred and thirty-six genes harbouring somatic mutations in this discovery set were sequenced in an additional 56 medulloblastomas. Recurrent mutations were detected in 41 genes not yet implicated in medulloblastoma; several target distinct components of the epigenetic machinery in different disease subgroups, such as regulators of H3K27 and H3K4 trimethylation in subgroups 3 and 4 (for example, KDM6A and ZMYM3), and CTNNB1-associated chromatin re-modellers in WNT-subgroup tumours (for example, SMARCA4 and CREBBP). Modelling of mutations in mouse lower rhombic lip progenitors that generate WNT-subgroup tumours identified genes that maintain this cell lineage (DDX3X), as well as mutated genes that initiate (CDH1) or cooperate (PIK3CA) in tumorigenesis. These data provide important new insights into the pathogenesis of medulloblastoma subgroups and highlight targets for therapeutic development.

Use of whole genome sequencing to identify novel mutations in distinct subgroups of medulloblastoma

9518

Background: Medulloblastoma is a malignant childhood brain tumor comprising four discrete subgroups (SHH-subgroup, WNT-subgroup, subgroup-3 and subgroup-4). The genetic alterations that drive these subgroups and that might serve as treatment targets are largely unknown. Methods: We sequenced entire genomes of 37 tumors and matched normal blood. 136 somatically mutated genes identified in this discovery cohort were sequenced in an additional 56 medulloblastomas. All tumors were classified into the 4 subgroups by expression profiling and immunohistochemistry. All mutations were validated by custom capture, 454, or Sanger sequencing. Results: Recurrent mutations were detected in 49 genes: 41 are not yet implicated in medulloblastoma. Several target distinct components of the epigenetic machinery in different disease subgroups, e.g., regulators of H3K27 and H3K4 trimethylation in subgroup-3 and 4 (e.g., KDM6A and ZMYM3), and CTNNB1-associated chromatin remodellers in WNT-subgroup tumors (e.g., SMARCA4 and CREBBP). Modelling of mutations in mouse lower rhombic lip progenitors that generate WNT-subgroup tumours, identified genes that maintain this cell lineage (DDX3X) as well as mutated genes that initiate (CDH1) or cooperate (PIK3CA) in tumourigenesis. Conclusions: We have identified several new recurrent somatic mutations that are enriched in specific subgroups of medulloblastoma. Alterations affecting subgroup-3 and 4 tumors appear to disrupt chromatin marking, most notably H3K27me3, potentially preserving a stem cell-like state in tumor cells. Mutations in WNT subgroup tumors affect binding partners of CTNNB1 that regulate WNT-response gene transcription. These data provide important new insights into the pathogenesis of medulloblastoma subgroups and highlight targets for therapeutic development.

Evolution of bacterial ribosomal protein L1

Search vectors composed of Gly, Ala, Arg, and Pro (GARP) residues retrieve 98% of each of the ribosomal proteins in prokaryotic species with no false hits. Different combinations of G, A, R and P and insertions differentiate each ribosomal protein from all others. Amino acids in two sequence positions separate Gram+ from Gram- bacteria. Specific residues separate proteins of cyanobacteria and chloroplasts from all other species. Structural information played an essential role in developing a GARP based technique to achieve perfect sequence alignment. It is possible to understand why GARP residues are 100% conserved in specific positions in families of proteins present in all species.

The short-chain oxidoreductase Q9HYA2 from Pseudomonas aeruginosa PAO1 contains an atypical catalytic center

The characteristic oxidation or reduction reaction mechanisms of short-chain oxidoreductase (SCOR) enzymes involve a highly conserved Asp-Ser-Tyr-Lys catalytic tetrad. The SCOR enzyme Q9HYA2 from the pathogenic bacterium Pseudomonas aeruginosa was recognized to possess an atypical catalytic tetrad composed of Lys118-Ser146-Thr159-Arg163. Orthologs of Q9HYA2 containing the unusual catalytic tetrad along with conserved substrate and cofactor recognition residues were identified in 27 additional species, the majority of which are bacterial pathogens. However, this atypical catalytic tetrad was not represented within the Protein Data Bank. The crystal structures of unligated and NADPH-complexed Q9HYA2 were determined at 2.3 A resolution. Structural alignment to a polyketide ketoreductase (KR), a typical SCOR, demonstrated that Q9HYA2's Lys118, Ser146, and Arg163 superimposed upon the KR's catalytic Asp114, Ser144, and Lys161, respectively. However, only the backbone of Q9HYA2's Thr159 overlapped KR's catalytic Tyr157. The Thr159 hydroxyl in apo Q9HYA2 is poorly positioned for participating in catalysis. In the Q9HYA2-NADPH complex, the Thr159 side chain was modeled in two alternate rotamers, one of which is positioned to interact with other members of the tetrad and the bound cofactor. A chloride ion is bound at the position normally occupied by the catalytic tyrosine hydroxyl. The putative active site of Q9HYA2 contains a chemical moiety at each catalytically important position of a typical SCOR enzyme. This is the first observation of a SCOR protein with this alternate catalytic center that includes threonine replacing the catalytic tyrosine and an ion replacing the hydroxyl moiety of the catalytic tyrosine.

Sequence fingerprint and structural analysis of the SCOR enzyme A3DFK9 from Clostridium thermocellum

We have identified a highly conserved fingerprint of 40 residues in the TGYK subfamily of the short-chain oxidoreductase enzymes. The TGYK subfamily is defined by the presence of an N-terminal TGxxxGxG motif and a catalytic YxxxK motif. This subfamily contains more than 12,000 members, with individual members displaying unique substrate specificities. The 40 fingerprint residues are critical to catalysis, cofactor binding, protein folding, and oligomerization but are substrate independent. Their conservation provides critical insight into evolution of the folding and function of TGYK enzymes. Substrate specificity is determined by distinct combinations of residues in three flexible loops that make up the substrate-binding pocket. Here, we report the structure determinations of the TGYK enzyme A3DFK9 from Clostridium thermocellum in its apo form and with bound NAD(+) cofactor. The function of this protein is unknown, but our analysis of the substrate-binding loops putatively identifies A3DFK9 as a carbohydrate or polyalcohol metabolizing enzyme. C. thermocellum has potential commercial applications because of its ability to convert biomaterial into ethanol. A3DFK9 contains 31 of the 40 TGYK subfamily fingerprint residues. The most significant variations are the substitution of a cysteine (Cys84) for a highly conserved glycine within a characteristic VNNAG motif, and the substitution of a glycine (Gly106) for a highly conserved asparagine residue at a helical kink. Both of these variations occur at positions typically participating in the formation of a catalytically important proton transfer network. An alternate means of stabilizing this proton wire was observed in the A3DFK9 crystal structures.