Christie Ingram

Performant Mutation Identification Using Targeted Next‐Generation Sequencing of 14 Thoracic Aortic Aneurysm Genes

At least 14 causative genes have been identified for both syndromic and nonsyndromic forms of thoracic aortic aneurysm/dissection (TAA), an important cause of death in the industrialized world. Molecular confirmation of the diagnosis is increasingly important for gene‐tailored patient management but consecutive, conventional molecular TAA gene screening is expensive and labor‐intensive. To circumvent these problems, we developed a TAA gene panel for next‐generation sequencing of 14 TAA genes. After validation, we applied the assay to 100 Marfan patients. We identified 90 FBN1 mutations, 44 of which were novel. In addition, Multiplex ligation‐dependent probe amplification identified large deletions in six of the remaining samples, whereas false‐negative results were excluded by Sanger sequencing of FBN1, TGFBR1, and TGFBR2 in the last four samples. Subsequently, we screened 55 syndromic and nonsyndromic TAA patients. We identified causal mutations in 15 patients (27%), one in each of the six following genes: ACTA2, COL3A1, TGFBR1, MYLK, SMAD3, SLC2A10 (homozygous), two in NOTCH1, and seven in FBN1. We conclude that our approach for TAA genetic testing overcomes the intrinsic hurdles of consecutive Sanger sequencing of all candidate genes and provides a powerful tool for the elaboration of clinical phenotypes assigned to different genes.

Exome sequencing implicates an increased burden of rare potassium channel variants in the risk of drug-induced long QT interval syndrome.

OBJECTIVES The aim of this study was to test the hypothesis that rare variants are associated with drug-induced long QT interval syndrome (diLQTS) and torsades de pointes. BACKGROUND diLQTS is associated with the potentially fatal arrhythmia torsades de pointes. The contribution of rare genetic variants to the underlying genetic framework predisposing to diLQTS has not been systematically examined. METHODS We performed whole-exome sequencing on 65 diLQTS patients and 148 drug-exposed control subjects of European descent. We used rare variant analyses (variable threshold and sequence kernel association test) and gene-set analyses to identify genes enriched with rare amino acid coding (AAC) variants associated with diLQTS. Significant associations were reanalyzed by comparing diLQTS patients with 515 ethnically matched control subjects from the National Heart, Lung, and Blood Grand Opportunity Exome Sequencing Project. RESULTS Rare variants in 7 genes were enriched in the diLQTS patients according to the sequence kernel association test or variable threshold compared with drug-exposed controls (p < 0.001). Of these, we replicated the diLQTS associations for KCNE1 and ACN9 using 515 Exome Sequencing Project control subjects (p < 0.05). A total of 37% of the diLQTS patients also had 1 or more rare AAC variants compared with 21% of control subjects (p = 0.009), in a pre-defined set of 7 congenital long QT interval syndrome (cLQTS) genes encoding potassium channels or channel modulators (KCNE1, KCNE2, KCNH2, KCNJ2, KCNJ5, KCNQ1, AKAP9). CONCLUSIONS By combining whole-exome sequencing with aggregated rare variant analyses, we implicate rare variants in KCNE1 and ACN9 as risk factors for diLQTS. Moreover, diLQTS patients were more burdened by rare AAC variants in cLQTS genes encoding potassium channel modulators, supporting the idea that multiple rare variants, notably across cLQTS genes, predispose to diLQTS.

Candidate gene approach to identifying rare genetic variants associated with lone atrial fibrillation

BACKGROUND Rare variants in candidate atrial fibrillation (AF) genes have been associated with AF in small kindreds. The extent to which such polymorphisms contribute to AF is unknown. OBJECTIVE The purpose of this study was to determine the spectrum and prevalence of rare amino acid coding (AAC) variants in candidate AF genes in a large cohort of unrelated lone AF probands. METHODS We resequenced 45 candidate genes in 303 European American (EA) lone AF probands (186 lone AF probands screened for each gene on average [range 89-303], 63 screened for all) identified in the Vanderbilt AF Registry (2002-2012). Variants detected were screened against 4300 EAs from the Exome Sequencing Project (ESP) to identify very rare (minor allele frequency ≤0.04%) AAC variants and these were tested for AF co-segregation in affected family members where possible. RESULTS Median age at AF onset was 46.0 years [interquartile range 33.0-54.0], and 35.6% had a family history of AF. Overall, 63 very rare AAC variants were identified in 60 of 303 lone AF probands, and 10 of 19 (52.6%) had evidence of co-segregation with AF. Among the 63 lone AF probands who had 45 genes screened, the very rare variant burden was 22%. Compared with the 4300 EA ESP, the proportion of lone AF probands with a very rare AAC variant in CASQ2 and NKX2-5 was increased 3-5-fold (P <.05). CONCLUSION No very rare AAC variants were identified in ~80% of lone AF probands. Potential reasons for the lack of very rare AAC variants include a complex pattern of inheritance, variants in as yet unidentified AF genes or in noncoding regions, and environmental factors.

A polymorphism in HLA-G modifies statin benefit in asthma

Several reports have shown that statin treatment benefits patients with asthma; however, inconsistent effects have been observed. The mir-152 family (148a, 148b and 152) has been implicated in asthma. These microRNAs suppress HLA-G expression, and rs1063320, a common SNP in the HLA-G 3′UTR that is associated with asthma risk, modulates miRNA binding. We report that statins upregulate mir-148b and 152, and affect HLA-G expression in an rs1063320-dependent fashion. In addition, we found that individuals who carried the G minor allele of rs1063320 had reduced asthma-related exacerbations (emergency department visits, hospitalizations or oral steroid use) compared with non-carriers (P=0.03) in statin users ascertained in the Personalized Medicine Research Project at the Marshfield Clinic (n=421). These findings support the hypothesis that rs1063320 modifies the effect of statin benefit in asthma, and thus may contribute to variation in statin efficacy for the management of this disease.

CYP2C19 and CES1 polymorphisms and efficacy of clopidogrel and aspirin dual antiplatelet therapy in patients with symptomatic intracranial atherosclerotic disease

OBJECT Symptomatic intracranial atherosclerotic disease (ICAD) has a high risk of recurrent stroke. Genetic polymorphisms in CYP2C19 and CES1 are associated with adverse outcomes in cardiovascular patients, but have not been studied in ICAD. The authors studied CYP2C19 and CES1 single-nucleotide polymorphisms (SNPs) in symptomatic ICAD patients. METHODS Genotype testing for CYP2C19*2, (*)3, (*)8, (*)17 and CES1 G143E was performed on 188 adult symptomatic ICAD patients from 3 medical centers who were medically managed with clopidogrel and aspirin. Testing was performed prospectively at 1 center, and retrospectively from a DNA sample biorepository at 2 centers. Multiple logistic regression and Cox regression analysis were performed to assess the association of these SNPs with the primary endpoint, which was a composite of transient ischemic attack (TIA), stroke, myocardial infarction, or death within 12 months. RESULTS The primary endpoint occurred in 14.9% of the 188 cases. In multiple logistic regression analysis, the presence of the CYP2C19 loss of function (LOF) alleles *2, *3, and *8 in the medically managed patients was associated with lower odds of primary endpoint compared with wild-type homozygotes (odds ratio [OR] 0.13, 95% CI 0.03-0.62, p = 0.0101). Cox regression analysis demonstrated the CYP2C19 LOF carriers had a lower risk for the primary endpoint, with hazard ratio (HR) of 0.27 (95% CI 0.08-0.95), p = 0.041. A sensitivity analysis of a secondary composite endpoint of TIA, stroke, or death demonstrated a significant trend in multiple logistic regression analysis of CYP2C19 variants, with lower odds of secondary endpoint in patients carrying at least 1 LOF allele (*2, *3, *8) than in wild-type homozygotes (OR 0.27, 95% CI 0.06-1.16, p = 0.078). Cox regression analysis demonstrated that the carriers of CYP2C19 LOF alleles had a lower risk forthe secondary composite endpoint (HR 0.22, 95% CI 0.05-1.04, p = 0.056). CONCLUSIONS This is the first study examining genetic variants and their effects in symptomatic ICAD. Variant alleles of CYP2C19 (*2, *3, *8) were associated with lower odds of the primary and secondary composite endpoints. However, the direction of the association was opposite of what is expected based on this SNP. This may reflect an incomplete understanding of this genetic variation and its effect in symptomatic ICAD and warrants further investigations.

CMTR1 is associated with increased asthma exacerbations in patients taking inhaled corticosteroids.

Inhaled corticosteroids (ICS) are the most effective controller medications for asthma, and variability in ICS response is associated with genetic variation. Despite ICS treatment, some patients with poor asthma control experience severe asthma exacerbations, defined as a hospitalization or emergency room visit. We hypothesized that some individuals may be at increased risk of asthma exacerbations, despite ICS use, due to genetic factors. A GWAS of 237,726 common, independent markers was conducted in 806 Caucasian asthmatic patients from two population‐based biobanks: BioVU, at Vanderbilt University Medical Center (VUMC) in Tennessee (369 patients), and Personalized Medicine Research Project (PMRP) at the Marshfield Clinic in Wisconsin (437 patients). Using a case–control study design, the association of each SNP locus with the outcome of asthma exacerbations (defined as asthma‐related emergency department visits or hospitalizations concurrent with oral corticosteroid use), was evaluated for each population by logistic regression analysis, adjusting for age, gender and the first four principal components. A meta‐analysis of the results was conducted. Validation of expression of selected candidate genes was determined by evaluating an independent microarray expression data set. Our study identified six novel SNPs associated with differential risk of asthma exacerbations (P < 10−05). The top GWAS result, rs2395672 in CMTR1, was associated with an increased risk of exacerbations in both populations (OR = 1.07, 95% CI 1.03–1.11; joint P = 2.3 × 10−06). Two SNPs (rs2395672 and rs279728) were associated with increased risk of exacerbations, while the remaining four SNPs (rs4271056, rs6467778, rs2691529, and rs9303988) were associated with decreased risk. Three SNPs (rs2395672, rs6467778, and rs2691529) were present in three genes: CMTR1, TRIM24 and MAGI2. The CMTR1 mRNA transcript was significantly differentially expressed in nasal lavage samples from asthmatics during acute exacerbations, suggesting potential involvement of this gene in the development of this phenotype. We show that genetic variability may contribute to asthma exacerbations in patients taking ICS. Furthermore, our studies implicate CMTR1 as a novel candidate gene with potential roles in the pathogenesis of asthma exacerbations.

Examining Rare and Low-Frequency Genetic Variants Previously Associated With Lone or Familial Forms of Atrial Fibrillation in an Electronic Medical Record System A Cautionary Note

Background—Studies in individuals or small kindreds have implicated rare variants in 25 different genes in lone and familial atrial fibrillation (AF) using linkage and segregation analysis, functional characterization, and rarity in public databases. Here, we used a cohort of 20 204 patients of European or African ancestry with electronic medical records and exome chip data to compare the frequency of AF among carriers and noncarriers of these rare variants. Methods and Results—The exome chip included 19 of 115 rare variants, in 9 genes, previously associated with lone or familial AF. Using validated algorithms querying a combination of clinical notes, structured billing codes, ECG reports, and procedure codes, we identified 1056 AF cases (>18 years) and 19 148 non-AF controls (>50 years) with available genotype data on the Illumina HumanExome BeadChip v.1.0 in the Vanderbilt electronic medical record-linked DNA repository, BioVU. Known correlations between AF and common variants at 4q25 were replicated. None of the 19 variants previously associated with AF were over-represented among AF cases (P>0.1 for all), and the frequency of variant carriers among non-AF controls was >0.1% for 14 of 19. Repeat analyses using non-AF controls aged >60 (n=14 904), >70 (n=9670), and >80 (n=4729) years did not influence these findings. Conclusions—Rare variants previously implicated in lone or familial forms of AF present on the exome chip are detected at low frequencies in a general population but are not associated with AF. These findings emphasize the need for caution when ascribing variants as pathogenic or causative.

Rare variants in genes encoding the cardiac sodium channel and associated compounds and their impact on outcome of catheter ablation of atrial fibrillation

Aim Rare variants of genes encoding the cardiac sodium channel and associated compounds have been linked with atrial fibrillation (AF). Nevertheless, current expert consensus does not support genetic testing in AF, which is in part based on the fact that “there is no therapeutic impact derived from AF genetic test results”. However, there are no studies available supporting this recommendation. Consequently, this study analyzed the impact of rare variants affecting the cardiac sodium channel on rhythm outcome of AF catheter ablation. Methods and results In 137 consecutive patients with lone AF enrolled in the Leipzig Heart Center AF ablation registry, screening for mutations in SCN5A, SCN1B – 4B, CAV3, GPD1L, SNTA1 and MOG1 was performed. We identified 3 rare non-synonymous variants in SCN5A, 5 in SCN1B, 1 in SCN4B, 1 in CAV3, 6 in GPD1L, 3 in SNTA1 and 3 in MOG1 (16%). Variant carriers were otherwise comparable with non-variant carriers. Analysis of AF recurrence rates after radiofrequency AF catheter ablation by serial 7-day Holter ECG monitoring between 3 and 12 months revealed no difference between groups, i.e. 45% in variant carriers vs. 49% in non-variant carriers. Conclusions Rare variants in genes encoding the cardiac sodium channel and associated compounds are frequently found in lone AF but were not found to impact the outcome of AF catheter ablation. This finding supports current recommendations not to screen for rare variants for the ablation outcome in AF. Nevertheless, it may at least be helpful for understanding AF mechanisms and larger studies are needed to further explore the possible association between genotype and response to AF therapies.

MUTATIONS IN GENES ENCODING THE CARDIAC SODIUM CHANNEL AND ASSOCIATED COMPOUNDS AND THEIR IMPACT ON OUTCOME OF CATHETER ABLATION FOR ATRIAL FIBRILLATION

Mutations in genes encoding the cardiac sodium channel and associated compounds have been linked with atrial fibrillation (AF). Nevertheless, current expert consensus does not support genetic testing in AF which is in part based on the fact that “there is no therapeutic impact derived from AF