Fragile X full mutation expansions are inhibited by one or more AGG interruptions in premutation carriers.

PURPOSE: Fragile X CGG repeat alleles often contain one or more AGG interruptions that influence allele stability and risk of a full mutation transmission from parent to child. We have examined transmissions of maternal and paternal alleles with 45-90 repeats to quantify the effect of AGG interruptions on fragile X repeat instability. METHODS: A novel FMR1 polymerase chain reaction assay was used to determine CGG repeat length and AGG interruptions for 1,040 alleles from 705 families. RESULTS: We grouped transmissions into nine categories of five repeats by parental size and found that in every size category, alleles with no AGGs had the greatest risk for instability. For maternal alleles <75 repeats, 89% (24/27) that expanded to a full mutation had no AGGs. Two contractions in maternal transmission were accompanied by loss of AGGs, suggesting a mechanism for generating alleles that lack AGG interruptions. Maternal age was examined as a factor in full mutation expansions using prenatal samples to minimize ascertainment bias, and a possible effect was observed though it was not statistically significant (P = 0.06). CONCLUSION: These results strengthen the association of AGG repeats with CGG repeat stability and provide more accurate risk estimates of full mutation expansions for women with 45-90 repeat alleles.

Profiling cancer gene mutations in clinical formalin-fixed, paraffin-embedded colorectal tumor specimens using targeted next-generation sequencing.

PURPOSE: The success of precision oncology relies on accurate and sensitive molecular profiling. The Ion AmpliSeq Cancer Panel, a targeted enrichment method for next-generation sequencing (NGS) using the Ion Torrent platform, provides a fast, easy, and cost-effective sequencing workflow for detecting genomic "hotspot" regions that are frequently mutated in human cancer genes. Most recently, the U.K. has launched the AmpliSeq sequencing test in its National Health Service. This study aimed to evaluate the clinical application of the AmpliSeq methodology. METHODS: We used 10 ng of genomic DNA from formalin-fixed, paraffin-embedded human colorectal cancer (CRC) tumor specimens to sequence 46 cancer genes using the AmpliSeq platform. In a validation study, we developed an orthogonal NGS-based resequencing approach (SimpliSeq) to assess the AmpliSeq variant calls. RESULTS: Validated mutational analyses revealed that AmpliSeq was effective in profiling gene mutations, and that the method correctly pinpointed "true-positive" gene mutations with variant frequency >5% and demonstrated high-level molecular heterogeneity in CRC. However, AmpliSeq enrichment and NGS also produced several recurrent "false-positive" calls in clinically druggable oncogenes such as PIK3CA. CONCLUSION: AmpliSeq provided highly sensitive and quantitative mutation detection for most of the genes on its cancer panel using limited DNA quantities from formalin-fixed, paraffin-embedded samples. For those genes with recurrent "false-positive" variant calls, caution should be used in data interpretation, and orthogonal verification of mutations is recommended for clinical decision making.

Differential expression of GNAS and KRAS mutations in pancreatic cysts.

CONTEXT: KRAS mutations play an important role in pancreatic cancer. GNAS mutations were discovered in intraductal papillary mucinous neoplasms (IPMN). OBJECTIVES: Our aim was to identify the frequency of KRAS and GNAS mutations in pancreatic cystic neoplasms and pancreatic ductal adenocarcinoma (PDAC). METHODS: Sixty-eight surgically resected formalin fixed, paraffin embedded pancreatic specimens were analyzed, including: 1) benign (20 serous cystadenoma (SCA)), 2) pre-malignant (10 mucinous cystic neoplasm (MCN), 10 branch duct intraductal papillary mucinous neoplasm (BD-IPMN), 9 main duct IPMN (MD-IPMN)), 3) malignant (19 PDAC). Total nucleic acid extraction was performed. KRAS codon 12/13 and GNAS codon 201 mutations were interrogated via targeted sequencing using the Ion Torrent's Personal Genome Machine (PGM). RESULTS: Mean age of 68 patients was 61.9±8.4 with 72% female. KRAS and GNAS mutations were more common in PDAC and IPMN. KRAS mutations predominated in PDAC compared to pancreatic cysts (16/19, 84% versus 10/49, 20%; P<0.001). GNAS mutations were more common in IPMN compared to non-IPMN lesions (8/19, 42% versus 2/49, 4%; P=0.0003). No GNAS mutations were detected in PDAC and MCN while 2 SCA carried GNAS mutations. Double mutations with KRAS and GNAS were only present in IPMN (5/19 versus 0/30 SCA and MCN, P=0.006). CONCLUSIONS: KRAS and GNAS mutations were more common in PDAC and IPMN with KRAS mutations primarily in PDAC and GNAS mutations more frequent in IPMN. No GNAS mutations occurred in MCN and double mutations were only present in IPMN.

Fragile X AGG analysis provides new risk predictions for 45-69 repeat alleles.

We investigated the effect of AGG interruptions on fragile X repeat instability upon transmission of fragile X intermediate and small premutation alleles with 45-69 CGG repeats. The FMR1 repeat structure was determined for 375 mothers, 48 fathers, and 538 offspring (457 maternal and 81 paternal transmissions) using a novel PCR assay to determine repeat length and AGG interruptions. The number of AGG interruptions and the length of uninterrupted CGG repeats at the 3' end were correlated with repeat instability on transmission. Maternal alleles with no AGGs conferred the greatest risk for unstable transmissions. All nine full mutation expansions were inherited from maternal alleles with no AGGs. Furthermore, the magnitude of repeat expansion was larger for alleles lacking AGG interruptions. Transmissions from paternal alleles with no AGGs also exhibited greater instability than those with one or more AGGs. Our results demonstrate that characterization of the AGG structure within the FMR1 repeat allows more accurate risk estimates of repeat instability and expansion to full mutations for intermediate and small premutation alleles.

High-resolution methylation polymerase chain reaction for fragile X analysis: evidence for novel FMR1 methylation patterns undetected in Southern blot analyses.

PURPOSE: Fragile X syndrome is associated with the expansion of CGG trinucleotide repeats and subsequent methylation of the FMR1 gene. Molecular diagnosis of fragile X currently requires Southern blot analysis to assess methylation. This study describes the evaluation of a polymerase chain reaction-only workflow for the determination of methylation status across a broad range of FMR1 genotypes in male and female specimens. METHODS: We evaluated a novel method that combines allele-specific methylation polymerase chain reaction and capillary electrophoresis with eight cell line and 80 clinical samples, including 39 full mutations. Methylation status was determined using a three-step workflow: (1) differential treatment of genomic DNA using a methylation-sensitive restriction enzyme; (2) polymerase chain reaction with two sets of dye-tagged primers; and (3) amplicon sizing by capillary electrophoresis. All samples were analyzed by both methylation polymerase chain reaction and Southern blot analysis. RESULTS: FMR1 methylation status and CGG repeat sizing were accurately and reproducibly determined in a set of methylation controls and genomic DNA samples representing a spectrum of CGG repeat lengths and methylation states. Moreover, methylation polymerase chain reaction revealed allele-specific methylation patterns in premutation alleles that were unobtainable using Southern blot analysis. CONCLUSIONS: Methylation polymerase chain reaction enabled high throughput, high resolution, and semiquantitative methylation assessments of FMR1 alleles, as well as determinations of CGG repeat length. Results for all samples were concordant with corresponding Southern blot analyses. As a result, this study presents a polymerase chain reaction-based method for comprehensive FMR1 analysis. In addition, the identification of novel methylation mosaic patterns revealed after polymerase chain reaction and capillary electrophoresis may be relevant to several FMR1 disorders.

A novel FMR1 PCR method for the routine detection of low abundance expanded alleles and full mutations in fragile X syndrome.

BACKGROUND: Fragile X syndrome (FXS) is a trinucleotide-repeat disease caused by the expansion of CGG sequences in the 5' untranslated region of the FMR1 (fragile X mental retardation 1) gene. Molecular diagnoses of FXS and other emerging FMR1 disorders typically rely on 2 tests, PCR and Southern blotting; however, performance or throughput limitations of these methods currently constrain routine testing. METHODS: We evaluated a novel FMR1 gene-specific PCR technology with DNA templates from 20 cell lines and 146 blinded clinical samples. The CGG repeat number was determined by fragment sizing of PCR amplicons with capillary electrophoresis, and results were compared with those for FMR1 Southern blotting analyses with the same samples. RESULTS: The FMR1 PCR accurately detected full-mutation alleles up to at least 1300 CGG repeats and consisting of >99% GC character. All categories of alleles detected by Southern blotting, including 66 samples with full mutations, were also identified by the FMR1 PCR for each of the 146 clinical samples. Because all full mutation alleles in samples from heterozygous females were detected by the PCR, allele zygosity was reconciled in every case. The PCR reagents also detected a 1% mass fraction of a 940-CGG allele in a background of 99% 23-CGG allele-a roughly 5- fold greater sensitivity than obtained with Southern blotting. CONCLUSIONS: The novel PCR technology can accurately categorize the spectrum of FMR1 alleles, including alleles previously considered too large to amplify; reproducibly detect low abundance full mutation alleles; and correctly infer homozygosity in female samples, thus greatly reducing the need for sample reflexing to Southern blotting.

Functional DNA quantification guides accurate next-generation sequencing mutation detection in formalin-fixed, paraffin-embedded tumor biopsies.

The formalin-fixed, paraffin-embedded (FFPE) biopsy is a challenging sample for molecular assays such as targeted next-generation sequencing (NGS). We compared three methods for FFPE DNA quantification, including a novel PCR assay ('QFI-PCR') that measures the absolute copy number of amplifiable DNA, across 165 residual clinical specimens. The results reveal the limitations of commonly used approaches, and demonstrate the value of an integrated workflow using QFI-PCR to improve the accuracy of NGS mutation detection and guide changes in input that can rescue low quality FFPE DNA. These findings address a growing need for improved quality measures in NGS-based patient testing.

Targeted, high-depth, next-generation sequencing of cancer genes in formalin-fixed, paraffin-embedded and fine-needle aspiration tumor specimens.

Implementation of highly sophisticated technologies, such as next-generation sequencing (NGS), into routine clinical practice requires compatibility with common tumor biopsy types, such as formalin-fixed, paraffin-embedded (FFPE) and fine-needle aspiration specimens, and validation metrics for platforms, controls, and data analysis pipelines. In this study, a two-step PCR enrichment workflow was used to assess 540 known cancer-relevant variants in 16 oncogenes for high-depth sequencing in tumor samples on either mature (Illumina GAIIx) or emerging (Ion Torrent PGM) NGS platforms. The results revealed that the background noise of variant detection was elevated approximately twofold in FFPE compared with cell line DNA. Bioinformatic algorithms were optimized to accommodate this background. Variant calls from 38 residual clinical colorectal cancer FFPE specimens and 10 thyroid fine-needle aspiration specimens were compared across multiple cancer genes, resulting in an accuracy of 96.1% (95% CI, 96.1% to 99.3%) compared with Sanger sequencing, and 99.6% (95% CI, 97.9% to 99.9%) compared with an alternative method with an analytical sensitivity of 1% mutation detection. A total of 45 of 48 samples were concordant between NGS platforms across all matched regions, with the three discordant calls each represented at <10% of reads. Consequently, NGS of targeted oncogenes in real-life tumor specimens using distinct platforms addresses unmet needs for unbiased and highly sensitive mutation detection and can accelerate both basic and clinical cancer research.

Performance evaluation of commercial miRNA expression array platforms.

BACKGROUND: microRNAs (miRNA) are short, endogenous transcripts that negatively regulate the expression of specific mRNA targets. The relative abundance of miRNAs is linked to function in vivo and miRNA expression patterns are potentially useful signatures for the development of diagnostic, prognostic and therapeutic biomarkers. FINDING: We compared the performance characteristics of four commercial miRNA array technologies and found that all platforms performed well in separate measures of performance. CONCLUSIONS: The Ambion and Agilent platforms were more accurate, whereas the Illumina and Exiqon platforms were more specific. Furthermore, the data analysis approach had a large impact on the performance, predominantly by improving precision.

An information-rich CGG repeat primed PCR that detects the full range of fragile X expanded alleles and minimizes the need for southern blot analysis.

(CGG)(n) repeat expansion in the FMR1 gene is associated with fragile X syndrome and other disorders. Current methods for FMR1 molecular testing rely on Southern blot analysis to detect expanded alleles too large to be PCR-amplified and to identify female homozygous alleles that often confound interpretations of PCR data. A novel, single-tube CGG repeat primed FMR1 PCR technology was designed with two gene-specific primers that flank the triplet repeat region, as well as a third primer that is complementary to the (CGG)(n) repeat. This PCR was evaluated with 171 unique DNA samples, including a blinded set of 146 clinical specimens. The method detected all alleles reported by Southern blot analysis, including full mutations in 66 clinical samples and comprised up to 1300 CGG. Furthermore, a blinded cohort of 42 female homozygous and heterozygous specimens, including 21 with full mutation alleles, was resolved with 100% accuracy. Last, AGG interrupter sequences, which may influence the risk of (CGG)(n) expansion in the children of some carriers, were each correctly identified in 14 male and female clinical samples as referenced to DNA sequencing. As a result, this PCR provides robust detection of expanded alleles and resolves allele zygosity, thus minimizing the number of samples that require Southern blot analysis and producing more comprehensive FMR1 genotyping data than other methods.