Exome capture reveals ZNF423 and CEP164 mutations, linking renal ciliopathies to DNA damage response signaling.

Nephronophthisis-related ciliopathies (NPHP-RC) are degenerative recessive diseases that affect kidney, retina, and brain. Genetic defects in NPHP gene products that localize to cilia and centrosomes defined them as "ciliopathies." However, disease mechanisms remain poorly understood. Here, we identify by whole-exome resequencing, mutations of MRE11, ZNF423, and CEP164 as causing NPHP-RC. All three genes function within the DNA damage response (DDR) pathway. We demonstrate that, upon induced DNA damage, the NPHP-RC proteins ZNF423, CEP164, and NPHP10 colocalize to nuclear foci positive for TIP60, known to activate ATM at sites of DNA damage. We show that knockdown of CEP164 or ZNF423 causes sensitivity to DNA damaging agents and that cep164 knockdown in zebrafish results in dysregulated DDR and an NPHP-RC phenotype. Our findings link degenerative diseases of the kidney and retina, disorders of increasing prevalence, to mechanisms of DDR.

Early Assessment of Cardiac Allograft Vasculopathy Risk Among Recipients of Hepatitis C Virus-infected Donors in the Current Era.

BACKGROUND: Transplantation of hearts from hepatitis C virus (HCV)-positive donors has increased substantially in recent years following development of highly effective direct-acting antiviral therapies for treatment and cure of HCV. Although historical data from the pre-direct-acting antiviral era demonstrated an association between HCV-positive donors and accelerated cardiac allograft vasculopathy (CAV) in recipients, the relationship between the use of HCV nucleic acid test-positive (NAT+) donors and the development of CAV in the direct-acting antiviral era remains unclear. METHODS AND RESULTS: We performed a retrospective, single-center observational study comparing coronary angiographic CAV outcomes during the first year after transplant in 84 heart transplant recipients of HCV NAT+ donors and 231 recipients of HCV NAT- donors. Additionally, in a subsample of 149 patients (including 55 in the NAT+ cohort and 94 in the NAT- cohort) who had serial adjunctive intravascular ultrasound examination performed, we compared development of rapidly progressive CAV, defined as an increase in maximal intimal thickening of ≥0.5 mm in matched vessel segments during the first year post-transplant. In an unadjusted analysis, recipients of HCV NAT+ hearts had reduced survival free of CAV ≥1 over the first year after heart transplant compared with recipients of HCV NAT- hearts. After adjustment for known CAV risk factors, however, there was no significant difference between cohorts in the likelihood of the primary outcome, nor was there a difference in development of rapidly progressive CAV. CONCLUSIONS: These findings support larger, longer-term follow-up studies to better elucidate CAV outcomes in recipients of HCV NAT+ hearts and to inform post-transplant management strategies.

Secular trends in success rate of catheter ablation for atrial fibrillation: The SMASH-AF cohort.

BACKGROUND: Approaches, tools, and technologies for atrial fibrillation (AF) ablation have evolved significantly since its inception. We sought to characterize secular trends in AF ablation success rates. METHODS: We performed a systematic review and meta-analysis of AF ablation from January 1, 1990, to August 1, 2016, searching PubMed, Scopus, and Cochrane databases. Major exclusion criteria were insufficient outcome reporting and ablation strategies that were not prespecified and uniform. We stratified treatment arms by AF type (paroxysmal AF; nonparoxysmal AF) and analyzed single-procedure outcomes. Multivariate meta-regressions analyzed effects of study, patient, and procedure characteristics on success rate trends. Registered in PROSPERO (CRD42016036549). RESULTS: A total of 180 trials and observational studies with 28,118 patients met inclusion. For paroxysmal AF ablation studies, unadjusted success rate summary estimates ranged from 73.1% in 2003 to 77.1% in 2016, increasing by 0.9%/year (95% CI 0.4%-1.4%; P = .001; I2 = 90%). After controlling for study design and patient demographics, rate of improvement in success rate summary estimate increased (1.6%/year; 95% CI 0.9%-2.2%; P = .001; I2 = 87%). For nonparoxysmal AF ablation studies, unadjusted success rate summary estimates ranged from 70.0% in 2010 to 64.3% in 2016 (1.1%/year; 95% CI -1.3% to 3.5%; P = .37; I2 = 85%), with no improvement in multivariate analyses. CONCLUSIONS: Despite substantial research investment and health care expenditure, improvements in AF ablation success rates have been incremental. Meaningful improvements may require major paradigm or technology changes, and evaluation of clinical outcomes such as mortality and quality of life may prove to be important going forward.

Urinary tract infection after catheter ablation of atrial fibrillation.

BACKGROUND: Urinary tract infection (UTI) is common after surgical procedures and a quality improvement target. For non-surgical procedures such as catheter ablation of atrial fibrillation (AF), UTI risk has not been characterized. We sought to determine incidence and risk factors of UTI after AF ablation and risk variation across sites. METHODS: Using Marketscan commercial claims databases, we performed a retrospective cohort study of patients who underwent AF ablation from 2007 to 2011. The primary outcome was UTI diagnosis within 30 days after ablation. We performed multivariate analyses to determine risk factors for UTI and risk of sepsis within 30 days after ablation with UTI as the predictor variable. Median odds ratio was used to quantify UTI site variation. RESULTS: Among 21 091 patients (age 59.2 ± 10.9; 29.1% female; CHA2 DS2 -VASc 2.0 ± 1.6), 622 (2.9%) were diagnosed with UTI within 30 days. In multivariate analyses, UTI was independently associated with age, female sex, prior UTI, and general anesthesia (all P < .01). UTI diagnosis was associated with a substantial increased risk of sepsis within 30 days (5.0% vs. 0.3%; odds ratio 17.5; 95% confidence interval [CI] 10.8-28.2; P < .0001). Among 416 sites, 211 had at least one UTI. Among these 211 sites, the incidence of postablation UTI ranged from 0.7 to 26.7% (median: 5.4%; Interquartile Range (IQR): 3.0-7.1%; 95th percentile: 14.3%; median odds ratio: 1.45; 95% CI 1.41-1.50). CONCLUSIONS: UTI after AF ablation is not uncommon and varies substantially across sites. Consideration of UTI as a quality measure and interventions targeted at high-risk patients or sites warrant consideration.

Geographic and racial representation and reported success rates of studies of catheter ablation for atrial fibrillation: Findings from the SMASH-AF meta-analysis study cohort.

INTRODUCTION: We performed a systematic review and meta-analysis of geographic and racial representation and reported success rates of studies of catheter ablation for atrial fibrillation (AF). METHODS AND RESULTS: We searched PubMed, Scopus, and Cochrane databases from 1/1/1990 to 8/1/2016 for trials and observational studies reporting AF ablation outcomes. Major exclusion criteria were insufficient reporting of outcomes, non-English language articles, and ablation strategies that were not prespecified and uniform. We described geographic and racial representation and single-procedure ablation success rates by country, controlling for patient demographics and study design characteristics. The analysis cohort included 306 studies (49,227 patients) from 28 countries. Over half of the paroxysmal (PAF) and nonparoxysmal AF (NPAF) treatment arms were conducted in 5 and 3 countries, respectively. Reporting of race or ethnicity demographics and outcomes were rare (1 study, 0.3%) and nonexistent, respectively. Unadjusted success rates by country ranged from 63.5% to 83.0% for PAF studies and 52.7% to 71.6% for NPAF studies, with substantial variation in patient demographics and study design. After controlling for covariates, South Korea and the United States had higher PAF ablation success rates, with large residual heterogeneity. NPAF ablation success rates were statistically similar by country. CONCLUSIONS: Studies of AF ablation have substantial variation in patient demographics, study design, and reported outcomes by country. There is limited geographic representation of trials and observational studies of AF ablation and a paucity of race- or ethnicity-stratified results. Future AF ablation studies and registries should aim to have broad representation by race, geography, and ethnicity to ensure generalizability.

Whole-exome resequencing distinguishes cystic kidney diseases from phenocopies in renal ciliopathies.

Rare single-gene disorders cause chronic disease. However, half of the 6000 recessive single gene causes of disease are still unknown. Because recessive disease genes can illuminate, at least in part, disease pathomechanism, their identification offers direct opportunities for improved clinical management and potentially treatment. Rare diseases comprise the majority of chronic kidney disease (CKD) in children but are notoriously difficult to diagnose. Whole-exome resequencing facilitates identification of recessive disease genes. However, its utility is impeded by the large number of genetic variants detected. We here overcome this limitation by combining homozygosity mapping with whole-exome resequencing in 10 sib pairs with a nephronophthisis-related ciliopathy, which represents the most frequent genetic cause of CKD in the first three decades of life. In 7 of 10 sibships with a histologic or ultrasonographic diagnosis of nephronophthisis-related ciliopathy, we detect the causative gene. In six sibships, we identify mutations of known nephronophthisis-related ciliopathy genes, while in two additional sibships we found mutations in the known CKD-causing genes SLC4A1 and AGXT as phenocopies of nephronophthisis-related ciliopathy. Thus, whole-exome resequencing establishes an efficient, noninvasive approach towards early detection and causation-based diagnosis of rare kidney diseases. This approach can be extended to other rare recessive disorders, thereby providing accurate diagnosis and facilitating the study of disease mechanisms.

Acute Sympathetic Blockade Improves Insulin-Mediated Microvascular Blood Flow in the Forearm of Adult Human Subjects With Obesity.

BACKGROUND: Obesity is associated with resistance to the metabolic (glucose uptake) and vascular (nitric-oxide mediated dilation and microvascular recruitment) actions of insulin. These vascular effects contribute to insulin sensitivity by increasing tissue delivery of glucose. Studies by us and others suggest that sympathetic activation contributes to insulin resistance to glucose uptake. Here we tested the hypothesis that sympathetic activation contributes to impaired insulin-mediated vasodilation in adult subjects with obesity. METHODS AND RESULTS: In a randomized crossover study, we used a euglycemic hyperinsulinemic clamp in 12 subjects with obesity to induce forearm arterial vasodilation (forearm blood flow) and microvascular recruitment (contrast-enhanced ultrasonography) during an intrabrachial infusion of saline (control) or phentolamine (sympathetic blockade). Insulin increased forearm blood flow on both study days (from 2.21±1.22 to 4.89±4.21 mL/100 mL per min, P=0.003 and from 2.42±0.89 to 7.19±3.35 mL/100 mL per min, P=0.002 for the intact and blocked day, respectively). Sympathetic blockade with phentolamine resulted in a significantly greater increase in microvascular flow velocity (∆microvascular flow velocity: 0.23±0.65 versus 2.51±3.01 arbitrary intensity units (AIU/s) for saline and phentolamine respectively, P=0.005), microvascular blood volume (∆microvascular blood volume: 1.69±2.45 versus 3.76±2.93 AIU, respectively, P=0.05), and microvascular blood flow (∆microvascular blood flow: 0.28±0.653 versus 2.51±3.01 AIU2/s, respectively, P=0.0161). To evaluate if this effect was not due to nonspecific vasodilation, we replicated the study in 6 subjects with obesity comparing intrabrachial infusion of phentolamine to sodium nitroprusside. At doses that produced similar increases in forearm blood flow, insulin-induced changes in microvascular flow velocity were greater during phentolamine than sodium nitroprusside (%microvascular flow velocity=58% versus 29%, respectively, P=0.031). CONCLUSIONS: We conclude that sympathetic activation impairs insulin-mediated microvascular recruitment in adult subjects with obesity.

Utility of Ischemia Testing Prior to Ablation for Sustained Monomorphic Ventricular Tachycardia.

The aim of this study was to determine the relationship between ischemia testing prior to ablation for sustained monomorphic ventricular tachycardia (VT) (SMVT) and post-ablation mortality and VT recurrence. As SMVT is generally caused by myocardial scar and not active ischemia, the utility of ischemia testing prior to SMVT ablation is unclear. Patients who underwent ablation for SMVT at 2 tertiary care centers between January 2016 and July 2018 were included in a retrospective study. A Kaplan-Meier survival analysis was performed, stratifying patients by pre-ablation ischemia testing for the endpoints of mortality and VT recurrence. A Cox multivariable regression analysis was performed to identify predictors of post-ablation VT recurrence. A total of 163 patients were included, with 46 (28%) patients undergoing ischemia testing prior to ablation. Only 5 of the 46 patients (11%) received revascularization pre-ablation. After a median follow-up period of 625 days (interquartile range, 292-982 days) following ablation, 97 of 163 patients (60%) had VT recurrence, and 32 patients (20%) had died. There was no difference in mortality or VT recurrence between patients who did or did not experience ischemia testing or revascularization. In the multivariable regression analysis, predictors of VT recurrence were the number of anti-arrhythmics failed, non-ischemic cardiomyopathy, sex, and cardiac magnetic resonance imaging pre-ablation. Neither ischemia testing nor revascularization was a significant predictor of VT recurrence in univariable or multivariable regression analysis. In conclusion, ischemia testing is frequently ordered prior to SMVT ablation but infrequently leads to revascularization and is not associated with post-ablation outcomes. The findings support adopting an individualized approach rather than performing routine ischemia testing.

Efficacy of Ablation Lesion Sets in Addition to Pulmonary Vein Isolation for Paroxysmal Atrial Fibrillation: Findings From the SMASH - AF Meta-Analysis Study Cohort.

Background The objective was to explore the efficacy of ablation lesion sets in addition to pulmonary vein isolation ( PVI ) for paroxysmal atrial fibrillation. The optimal strategy for catheter ablation of paroxysmal atrial fibrillation is debated. Methods and Results The SMASH-AF (Systematic Review and Meta-analysis of Ablation Strategy Heterogeneity in Atrial Fibrillation) study cohort includes trials and observational studies identified in PubMed, Scopus, and Cochrane databases from January 1 1990, to August 1, 2016. We included studies reporting single procedure paroxysmal atrial fibrillation ablation success rates. Exclusion criteria included insufficient reporting of outcomes, ablation strategies that were not prespecified and uniform, and a sample size of fewer than 40 patients. We analyzed lesion sets performed in addition to PVI ( PVI plus) using multivariable random-effects meta-regression to control for patient, study, and procedure characteristics. The analysis included 145 total studies with 23 263 patients ( PVI- only cohort: 115 studies, 148 treatment arms, 16 500 patients; PVI plus cohort: 39 studies; 46 treatment arms, 6763 patients). PVI plus studies, as compared with PVI -only studies, included younger patients (56.7 years versus 58.8 years, P=0.001), fewer women (27.2% versus 32.0% women, P=0.002), and were more methodologically rigorous with longer follow-up (29.5 versus 17.1 months, P 0.004) and more randomization (19.4% versus 11.8%, P<0.001). In multivariable meta-regression, PVI plus studies were associated with improved success (7.6% absolute improvement [95% CI, 2.6-12.5%]; P<0.01, I2=88%), specifically superior vena cava isolation (4 studies, 4 treatment arms, 1392 patients; 15.1% absolute improvement [95% CI, 2.3-27.9%]; P 0.02, I2=87%). However, residual heterogeneity was large. Conclusions Across the paroxysmal atrial fibrillation ablation literature, PVI plus ablation strategies were associated with incremental improvements in success rate. However, large residual heterogeneity complicates evidence synthesis.

CEP41 is mutated in Joubert syndrome and is required for tubulin glutamylation at the cilium.

Tubulin glutamylation is a post-translational modification that occurs predominantly in the ciliary axoneme and has been suggested to be important for ciliary function. However, its relationship to disorders of the primary cilium, termed ciliopathies, has not been explored. Here we mapped a new locus for Joubert syndrome (JBTS), which we have designated as JBTS15, and identified causative mutations in CEP41, which encodes a 41-kDa centrosomal protein. We show that CEP41 is localized to the basal body and primary cilia, and regulates ciliary entry of TTLL6, an evolutionarily conserved polyglutamylase enzyme. Depletion of CEP41 causes ciliopathy-related phenotypes in zebrafish and mice and results in glutamylation defects in the ciliary axoneme. Our data identify CEP41 mutations as a cause of JBTS and implicate tubulin post-translational modification in the pathogenesis of human ciliary dysfunction.

FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair.

Chronic kidney disease (CKD) represents a major health burden. Its central feature of renal fibrosis is not well understood. By exome sequencing, we identified mutations in FAN1 as a cause of karyomegalic interstitial nephritis (KIN), a disorder that serves as a model for renal fibrosis. Renal histology in KIN is indistinguishable from that of nephronophthisis, except for the presence of karyomegaly. The FAN1 protein has nuclease activity and acts in DNA interstrand cross-link (ICL) repair within the Fanconi anemia DNA damage response (DDR) pathway. We show that cells from individuals with FAN1 mutations have sensitivity to the ICL-inducing agent mitomycin C but do not exhibit chromosome breakage or cell cycle arrest after diepoxybutane treatment, unlike cells from individuals with Fanconi anemia. We complemented ICL sensitivity with wild-type FAN1 but not with cDNA having mutations found in individuals with KIN. Depletion of fan1 in zebrafish caused increased DDR, apoptosis and kidney cysts. Our findings implicate susceptibility to environmental genotoxins and inadequate DNA repair as novel mechanisms contributing to renal fibrosis and CKD.