Andrew L. Lundquist

KCNH2-K897T Is a Genetic Modifier of Latent Congenital Long-QT Syndrome

Background—Clinical heterogeneity among patients with long-QT syndrome (LQTS) sharing the same disease-causing mutation is usually attributed to variable penetrance. One potential explanation for this phenomenon is the coexistence of modifier gene alleles, possibly common single nucleotide polymorphisms, altering arrhythmia susceptibility. We demonstrate this concept in a family segregating a novel, low-penetrant KCNH2 mutation along with a common single nucleotide polymorphism in the same gene. Methods and Results—The proband is a 44-year-old white woman with palpitations associated with presyncope since age 20, who presented with ventricular fibrillation and cardiac arrest. Intermittent QT prolongation was subsequently observed (max QTc, 530 ms), and LQT2 was diagnosed after the identification of a missense KCNH2 mutation (A1116V) altering a conserved residue in the distal carboxyl-terminus of the encoded HERG protein. The proband also carried the common KCNH2 polymorphism K897T on the nonmutant allele. Relatives who carried A1116V without K897T were asymptomatic, but some exhibited transient mild QTc prolongation, suggesting latent disease. Heterologous expression studies performed in cultured mammalian cells and using bicistronic vectors linked to different fluorescent proteins demonstrated that coexpression of A1116V with K897T together resulted in significantly reduced current amplitude as compared with coexpression of either allele with WT-HERG. Thus, the presence of KCNH2-K897T is predicted to exaggerate the IKr reduction caused by the A1116V mutation. These data explain why symptomatic LQTS occurred only in the proband carrying both alleles. Conclusions—We have provided evidence that a common KCNH2 polymorphism may modify the clinical expression of a latent LQT2 mutation. A similar mechanism may contribute to the risk for sudden death in more prevalent cardiac diseases.

Phenotypic Variability and Unusual Clinical Severity of Congenital Long-QT Syndrome in a Founder Population

Background— In the congenital long-QT syndrome (LQTS), there can be a marked phenotypic heterogeneity. Founder effects, by which many individuals share a mutation identical by descent, represent a powerful tool to further understand the underlying mechanisms and to predict the natural history of mutation-associated effects. We are investigating one such founder effect, originating in South Africa in approximately ad 1700 and segregating the same KCNQ1 mutation (A341V). Methods and Results— The study population involved 320 subjects, 166 mutation carriers (MCs) and 154 noncarriers. When not taking β-blocker therapy, MCs had a wide range of QTc values (406 to 676 ms), and 12% of individuals had a normal QTc (≤440 ms). A QTc >500 ms was associated with increased risk for cardiac events (OR=4.22; 95% CI, 1.12 to 15.80; P=0.033). We also found that MCs with a heart rate <73 bpm were at significantly lower risk (OR=0.23; 95% CI, 0.06 to 0.86; P=0.035). This study also unexpectedly determined that KCNQ1-A341V is associated with greater risk than that reported for large databases of LQT1 patients: A341V MCs are more symptomatic by age 40 years (79% versus 30%) and become symptomatic earlier (7±4 versus 13±9 years, both P<0.001). Accordingly, functional studies of KCNQ1-A341V in CHO cells stably expressing IKs were conducted and identified a dominant negative effect of the mutation on wild-type channels. Conclusions— KCNQ1-A341V is a mutation associated with an unusually severe phenotype, most likely caused by the dominant negative effect of the mutation. The availability of an extended kindred with a common mutation allowed us to identify heart rate, an autonomic marker, as a novel risk factor.

Treatment of hepatitis C virus–associated mixed cryoglobulinemia with direct-acting antiviral agents

Hepatitis C virus (HCV) is the most common cause of mixed cryoglobulinemia syndrome (MCS). The efficacy and safety of all‐oral direct‐acting antiviral (DAA) therapy in HCV‐associated MCS (HCV‐MCS) is largely unknown. The authors studied case series of patients with HCV‐MCS who were treated with sofosbuvir‐based regimens and historical controls treated with pegylated interferon and ribavirin in a single health care network. HCV‐MCS was defined by circulating cryoglobulin associated with systemic vasculitis symptoms. Renal involvement (n = 7) was established by kidney biopsy (n = 5) or by two or more of the following clinical findings: reduced kidney function, proteinuria, or hematuria with other causes excluded (n = 2). Twelve patients received DAA therapy between December 2013 and September 2014. Median age was 61 years, 58% were male, and 50% had cirrhosis. Median baseline serum creatinine was 0.97 mg/dL (range 0.7‐2.47). Four patients received rituximab concurrent with DAA therapy. Sustained virological response rate at 12 weeks (SVR12) was 83% overall. Patients with glomerulonephritis who achieved SVR12 experienced an improvement in serum creatinine and a reduction in proteinuria. Cryoglobulin levels decreased in 89% of patients, with median percent decreasing from 1.5% to 0.5% and completely disappearing in four of nine cases who had cryoglobulins measured after treatment. Serious adverse events were infrequent (17%). In contrast, the historical cohort treated with pegylated interferon and ribavirin experienced only 10% SVR12, with 100% experiencing at least one adverse event and 50% experiencing premature discontinuation due to adverse events. Conclusion: SVR12 rates for sofosbuvir‐based DAA regimens in HCV‐MCS were 83%, significantly higher than historical controls treated with pegylated interferon and ribavirin; patients with glomerulonephritis experienced improvement in renal function, including those not concomitantly treated with immunosuppression. (Hepatology 2016;63:408–417)

An improved canine genome and a comprehensive catalogue of coding genes and non-coding transcripts.

The domestic dog, Canis familiaris, is a well-established model system for mapping trait and disease loci. While the original draft sequence was of good quality, gaps were abundant particularly in promoter regions of the genome, negatively impacting the annotation and study of candidate genes. Here, we present an improved genome build, canFam3.1, which includes 85 MB of novel sequence and now covers 99.8% of the euchromatic portion of the genome. We also present multiple RNA-Sequencing data sets from 10 different canine tissues to catalog ∼175,000 expressed loci. While about 90% of the coding genes previously annotated by EnsEMBL have measurable expression in at least one sample, the number of transcript isoforms detected by our data expands the EnsEMBL annotations by a factor of four. Syntenic comparison with the human genome revealed an additional ∼3,000 loci that are characterized as protein coding in human and were also expressed in the dog, suggesting that those were previously not annotated in the EnsEMBL canine gene set. In addition to ∼20,700 high-confidence protein coding loci, we found ∼4,600 antisense transcripts overlapping exons of protein coding genes, ∼7,200 intergenic multi-exon transcripts without coding potential, likely candidates for long intergenic non-coding RNAs (lincRNAs) and ∼11,000 transcripts were reported by two different library construction methods but did not fit any of the above categories. Of the lincRNAs, about 6,000 have no annotated orthologs in human or mouse. Functional analysis of two novel transcripts with shRNA in a mouse kidney cell line altered cell morphology and motility. All in all, we provide a much-improved annotation of the canine genome and suggest regulatory functions for several of the novel non-coding transcripts.

Fibroblast Growth Factor 23 in Patients Undergoing Peritoneal Dialysis

BACKGROUND AND OBJECTIVES Fibroblast growth factor 23 (FGF23) is an independent risk factor for mortality in patients with ESRD. Before FGF23 testing can be integrated into clinical practice of ESRD, further understanding of its determinants is needed. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS In a study of 67 adults undergoing peritoneal dialysis, we tested the hypothesis that longer dialysis vintage and lower residual renal function and renal phosphate clearance are associated with higher FGF23. We also compared the monthly variability of FGF23 versus parathyroid hormone (PTH) and serum phosphate. RESULTS In unadjusted analyses, FGF23 correlated with serum phosphate (r = 0.66, P < 0.001), residual renal function (r = -0.37, P = 0.002), dialysis vintage (r = 0.31, P = 0.01), and renal phosphate clearance (r = -0.38, P = 0.008). In adjusted analyses, absence of residual renal function and greater dialysis vintage associated with higher FGF23, independent of demographics, laboratory values, peritoneal dialysis modality and adequacy, and treatment with vitamin D analogs and phosphate binders. Urinary and dialysate FGF23 clearances were minimal. In three serial monthly measurements, within-subject variability accounted for only 10% of total FGF23 variability compared with 50% for PTH and 60% for serum phosphate. CONCLUSIONS Increased serum phosphate, loss of residual renal function, longer dialysis vintage, and lower renal phosphate clearance are associated with elevated FGF23 levels in ESRD patients undergoing peritoneal dialysis. FGF23 may be a more stable marker of phosphate metabolism in ESRD than PTH or serum phosphate.

Serum sickness following rabbit antithymocyte-globulin induction in a liver transplant recipient : Case report and literature review

Thymoglobulin® (Genzyme, Cambridge, MA) is an antithymocyte globulin preparation used for induction immunosuppression therapy in solid organ transplantation. It is being utilized with increasing frequency in orthotopic liver transplantation (OLT) in an effort to minimize or delay the use of calcineurin inhibitors due to their inherent nephrotoxicity. Experience with thymoglobulin in OLT remains limited. We report a case of serum sickness in a patient who received thymoglobulin following OLT. The patient experienced intermittent fevers, polyarthralgia, and acute renal failure 9 days after completion of thymoglobulin administration. The patients symptoms resolved rapidly and completely with a course of intravenous steroids. We review a set of diagnostic criteria for serum sickness and emphasize the importance of early recognition of the process. Early treatment of serum sickness with steroids or plasmapheresis is highly effective and can reduce unnecessary morbidity from this unusual sequela of induction immunosuppression with antithymocyte globulin. Liver Transpl.

Reduced expression of Kir6.2/SUR2A subunits explains KATP deficiency in K+-depleted rats.

We investigated on the mechanism responsible for the reduced ATP-sensitive K(+)(K(ATP)) channel activity recorded from skeletal muscle of K(+)-depleted rats. Patch-clamp and gene expression measurements of K(ATP) channel subunits were performed. A down-regulation of the K(ATP) channel subunits Kir6.2(-70%) and SUR2A(-46%) in skeletal muscles of K(+)-depleted rats but no changes in the expression of Kir6.1, SUR1 and SUR2B subunits were observed. A reduced K(ATP) channel currents of -69.5% in K(+)-depleted rats was observed. The Kir6.2/SUR2A-B agonist cromakalim showed similar potency in activating the K(ATP) channels of normokalaemic and K(+)-depleted rats but reduced efficacy in K(+)-depleted rats. The Kir6.2/SUR1-2B agonist diazoxide activated K(ATP) channels in normokalaemic and K(+)-depleted rats with equal potency and efficacy. The down-regulation of the Kir6.2 explains the reduced K(ATP) channel activity in K(+)-depleted rats. The lower expression of SUR2A explains the reduced efficacy of cromakalim; preserved SUR1 expression accounts for the efficacy of diazoxide. Kir6.2/SUR2A deficiency is associated with impaired muscle function in K(+)-depleted rats and in hypoPP.

Lupus-like Immune Complex-mediated Glomerulonephritis in Patients with Hepatitis C Virus Infection Treated with Oral, Interferon-free, Direct-acting Antiviral Therapy.

Novel, all-oral interferon-free direct-acting antiviral agents have revolutionized the management of hepatitis C virus (HCV) infection by producing exceptional cure rates with minimal adverse events. While provocation or exacerbation of autoimmunity has been reported in HCV-infected patients receiving interferon, this phenomenon has not been reported in patients receiving interferon-free HCV therapy. We report the occurrence of three cases of lupus-like immune complex-mediated glomerulonephritis occurring shortly after exposure to sofosbuvir-based direct-acting antiviral therapies. In all three cases, renal function quickly improved with immunosuppression. However, two of the three patients developed infectious complications of immunosuppression and died. This is the first report of a lupus-like immune complex mediated glomerulonephritis occurring in the context of HCV eradication with all-oral direct-acting antiviral therapies.

The Usefulness of Diagnostic Testing in the Initial Evaluation of Chronic Kidney Disease

Chronic kidney disease (CKD) affects approximately 13% of adults in the United States and is associated with significant morbidity, mortality, and costs.1–3 There is a broad differential for CKD, including diabetes mellitus, hypertension, glomerulonephritis, tubulointerstitial disease, urologic causes, and unknown causes.2 To our knowledge, a comprehensive assessment of the tests used in CKD evaluation has not been conducted. We determined how often laboratory and imaging tests were obtained in the initial evaluation of CKD and whether these tests affected diagnosis and/or management.

Optimal management of bone mineral disorders in chronic kidney disease and end stage renal disease.

Purpose of reviewThe review summarizes recent studies on chronic kidney disease–mineral bone disorders, with a focus on new developments in disease management. Recent findingsThe term chronic kidney disease–mineral bone disorder has come to describe an increasingly complex network of alterations in minerals and skeletal disorders that contribute to the significant cardiovascular morbidity and mortality seen in patients with chronic kidney disease and end stage renal disease. Clinical studies continue to suggest associations with clinical outcomes, yet current clinical trials have failed to support causality. Variability in practice exists as current guidelines for management of mineral bone disorders are often based on weak evidence. Recent studies implicate novel pathways for therapeutic intervention in clinical trials. SummaryMineral bone disorders in chronic kidney disease arise from alterations in a number of molecules in an increasingly complex physiological network interconnecting bone and the cardiovascular system. Despite extensive associations with improved outcomes in a number of molecules, clinical trials have yet to prove causality and there is an absence of new therapies available to improve patient outcomes. Additional clinical trials that can incorporate the complexity of mineral bone disorders, and with the ability to intervene on more than one pathway, are needed to advance patient care.