Clinical characterization of type 1 long QT syndrome caused by C-terminus Kv7.1 variants

BACKGROUND

Variants in the KCNQ1 gene, encoding the α-subunit of the slow component of delayed rectifier K+ channel Kv7.1, cause long QT syndrome (LQTS) type 1. The location of variants may be one of the factors in determining prognosis. However, detailed genotype-phenotype relationships associated with C-terminus variants remain unelucidated.

OBJECTIVE

We investigated the clinical characteristics and variant-specific arrhythmic risks in patients with LQTS carrying Kv7.1 C-terminus variants.

METHODS

The study comprises 202 consecutive patients with LQTS (98 probands and 104 family members) who carry a rare heterozygous variant in the Kv7.1 C-terminus. Their clinical characteristics and arrhythmic events were investigated.

RESULTS

We identified 36 unique C-terminus variants (25 missense and 11 non-missense). The p.R366W variant was identified in 8 families, and p.T587M was identified in 21 families in large numbers from northwestern Japan. As for the location of the variant, we found that the variants in highly conserved regions and nonhelical domains were associated with longer QTc intervals compared with the variants in other regions. Both p.R366W and p.T587M variants are located in the highly conserved and functionally pivotal regions close to helices A and D, which are associated with calmodulin binding and channel assembly (tetramerization), respectively. The probands carrying p.T587M and p.R366W variants had worse arrhythmia outcomes compared with those with other C-terminus variants. The haplotype analysis of p.T587M families was suggestive of a founder effect.

CONCLUSION

The arrhythmic risk of C-terminus variants in Kv7.1 in LQTS is not homogeneous, and locations of variants can be a determining factor for prognosis.

Holter Electrocardiographic Approach to Predicting Outcomes of Pediatric Patients With Long QT Syndrome

BACKGROUND

This study was performed to clarify the clinical findings of pediatric patients diagnosed with long QT syndrome (LQTS) through electrocardiographic screening programs and to predict their outcome using Holter electrocardiographic approaches.Methods and Results: This retrospective study included pediatric patients with a Schwartz score of ≥3.5 who visited the National Hospital Organization Kagoshima Medical Center between April 2005 and March 2019. Resting 12-lead and Holter electrocardiograms were recorded at every visit. The maximum resting QTc and maximum Holter QTc values among all recordings were used for statistical analyses. To test the prognostic value of QTc for the appearance of cardiac events after the first hospital visit, receiver operating characteristic curves were used to calculate the area under the curve (AUC). Among 207 patients, 181 (87%) were diagnosed through screening programs. The prevalence of cardiac events after the first hospital visit was 4% (8/207). Among QTc at diagnosis, maximum resting QTc, and maximum Holter QTc, only maximum Holter QTc value was a predictor (P=0.02) of cardiac events after the hospital visit in multivariate regression analysis. The AUC of the maximum Holter QTc was significantly superior to that of maximum resting QTc.

CONCLUSIONS

The maximum Holter QTc value can be used to predict the appearance of symptoms in pediatric patients with LQTS.

Calmodulinopathy in Japanese Children - Their Cardiac Phenotypes Are Severe and Show Early Onset in Fetal Life and Infancy

BACKGROUND

Cardiac calmodulinopathy, characterized by a life-threatening arrhythmia and sudden death in the young, is extremely rare and caused by genes encoding calmodulin, namely calmodulin 1 (CALM1), CALM2, and CALM3.Methods and Results: We screened 195 symptomatic children (age 0-12 years) who were suspected of inherited arrhythmias for 48 candidate genes, using a next-generation sequencer. Ten probands were identified as carrying variants in any of CALM1-3 (5%; median age 5 years), who were initially diagnosed with long QT syndrome (LQTS; n=5), catecholaminergic polymorphic ventricular tachycardia (CPVT; n=3), and overlap syndrome (n=2). Two probands harbored a CALM1 variant and 8 probands harbored 6 CALM2 variants. There were 4 clinical phenotypes: (1) documented lethal arrhythmic events (LAEs): 4 carriers of N98S in CALM1 or CALM2; (2) suspected LAEs: CALM2 p.D96G and D132G carriers experienced syncope and transient cardiopulmonary arrest under emotional stimulation; (3) critical cardiac complication: CALM2 p.D96V and p.E141K carriers showed severe cardiac dysfunction with QTc prolongation; and (4) neurological and developmental disorders: 2 carriers of CALM2 p.E46K showed cardiac phenotypes of CPVT. Beta-blocker therapy was effective in all cases except cardiac dysfunction, especially in combination with flecainide (CPVT-like phenotype) and mexiletine (LQTS-like).

CONCLUSIONS

Calmodulinopathy patients presented severe cardiac features, and their onset of LAEs was earlier in life, requiring diagnosis and treatment at the earliest age possible.

Clinical presentation of calmodulin mutations: the International Calmodulinopathy Registry

AIMS

Calmodulinopathy due to mutations in any of the three CALM genes (CALM1-3) causes life-threatening arrhythmia syndromes, especially in young individuals. The International Calmodulinopathy Registry (ICalmR) aims to define and link the increasing complexity of the clinical presentation to the underlying molecular mechanisms.

METHODS AND RESULTS

The ICalmR is an international, collaborative, observational study, assembling and analysing clinical and genetic data on CALM-positive patients. The ICalmR has enrolled 140 subjects (median age 10.8 years [interquartile range 5-19]), 97 index cases and 43 family members. CALM-LQTS and CALM-CPVT are the prevalent phenotypes. Primary neurological manifestations, unrelated to post-anoxic sequelae, manifested in 20 patients. Calmodulinopathy remains associated with a high arrhythmic event rate (symptomatic patients, n = 103, 74%). However, compared with the original 2019 cohort, there was a reduced frequency and severity of all cardiac events (61% vs. 85%; P = .001) and sudden death (9% vs. 27%; P = .008). Data on therapy do not allow definitive recommendations. Cardiac structural abnormalities, either cardiomyopathy or congenital heart defects, are present in 30% of patients, mainly CALM-LQTS, and lethal cases of heart failure have occurred. The number of familial cases and of families with strikingly different phenotypes is increasing.

CONCLUSION

Calmodulinopathy has pleiotropic presentations, from channelopathy to syndromic forms. Clinical severity ranges from the early onset of life-threatening arrhythmias to the absence of symptoms, and the percentage of milder and familial forms is increasing. There are no hard data to guide therapy, and current management includes pharmacological and surgical antiadrenergic interventions with sodium channel blockers often accompanied by an implantable cardioverter-defibrillator.

FFR-CT is extremely useful in detecting hemodynamically significant left-main coronary artery stenosis with right coronary artery hypoplasia: A case report

Left main coronary artery (LMCA) stenosis in patients with coronary artery disease (CAD) is associated with a significant increase in cardiac events, and determining its contribution to ischemia is essential. Currently, several noninvasive modalities are available for the ischemic assessment of CAD. In multi-vessel disease, including LMCA disease, the accuracy of myocardial perfusion scintigraphy (MPS) for detecting myocardial ischemia can be poor. Fractional flow reserve from computed tomography (FFR-CT) has emerged as a promising noninvasive modality that can provide functional myocardial ischemia information. Herein, we describe the case of a 50-year-old woman with type 2 diabetes who presented to the hospital due to intermittent chest pain on exertion. Coronary computed tomography angiography showed right coronary artery hypoplasia, 25 % stenosis in the LMCA, and 75 % stenosis in the left anterior descending. FFR-CT identified myocardial ischemia due to LMCA stenosis, but MPS did not. Invasive coronary angiography with conventional fractional flow reserve was mostly consistent with the results of FFR-CT.

Learning objective

Fractional flow reserve from computed tomography (FFR-CT), which is a novel noninvasive method, can provide absolute, not relative, functional myocardial ischemia information by applying computational fluid dynamics to coronary computed tomography angiography on a lesion-by-lesion basis. FFR-CT can be extremely useful in detecting patients with left main coronary artery stenosis with right coronary artery hypoplasia.

Non-missense variants of KCNH2 show better outcomes in type 2 long QT syndrome

AIMS

More than one-third of type 2 long QT syndrome (LQT2) patients carry KCNH2 non-missense variants that can result in haploinsufficiency (HI), leading to mechanistic loss-of-function. However, their clinical phenotypes have not been fully investigated. The remaining two-thirds of patients harbour missense variants, and past studies uncovered that most of these variants cause trafficking deficiency, resulting in different functional changes: either HI or dominant-negative (DN) effects. In this study, we examined the impact of altered molecular mechanisms on clinical outcomes in LQT2 patients.

METHODS AND RESULTS

We included 429 LQT2 patients (234 probands) carrying a rare KCNH2 variant from our patient cohort undergoing genetic testing. Non-missense variants showed shorter corrected QT (QTc) and less arrhythmic events (AEs) than missense variants. We found that 40% of missense variants in this study were previously reported as HI or DN. Non-missense and HI-groups had similar phenotypes, while both exhibited shorter QTc and less AEs than the DN-group. Based on previous work, we predicted the functional change of the unreported variants-whether they cause HI or DN via altered functional domains-and stratified them as predicted HI (pHI)- or pDN-group. The pHI-group including non-missense variants exhibited milder phenotypes compared to the pDN-group. Multivariable Cox model showed that the functional change was an independent risk of AEs (P = 0.005).

CONCLUSION

Stratification based on molecular biological studies enables us to better predict clinical outcomes in the patients with LQT2.

Novel Calmodulin Variant p.E46K Associated With Severe Catecholaminergic Polymorphic Ventricular Tachycardia Produces Robust Arrhythmogenicity in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

BACKGROUND

CaM (calmodulin) is a ubiquitously expressed, multifunctional Ca²⁺ sensor protein that regulates numerous proteins. Recently, CaM missense variants have been identified in patients with malignant inherited arrhythmias, such as long QT syndrome and catecholaminergic polymorphic ventricular tachycardia (CPVT). However, the exact mechanism of CaM-related CPVT in human cardiomyocytes remains unclear. In this study, we sought to investigate the arrhythmogenic mechanism of CPVT caused by a novel variant using human induced pluripotent stem cell (iPSC) models and biochemical assays.

METHODS

We generated iPSCs from a patient with CPVT bearing CALM2 p.E46K. As comparisons, we used 2 control lines including an isogenic line, and another iPSC line from a patient with long QT syndrome bearing CALM2 p.N98S (also reported in CPVT). Electrophysiological properties were investigated using iPSC-cardiomyocytes. We further examined the RyR2 (ryanodine receptor 2) and Ca²⁺ affinities of CaM using recombinant proteins.

RESULTS

We identified a novel de novo heterozygous variant, CALM2 p.E46K, in 2 unrelated patients with CPVT accompanied by neurodevelopmental disorders. The E46K-cardiomyocytes exhibited more frequent abnormal electrical excitations and Ca²⁺ waves than the other lines in association with increased Ca²⁺ leakage from the sarcoplasmic reticulum via RyR2. Furthermore, the [³H]ryanodine binding assay revealed that E46K-CaM facilitated RyR2 function especially by activating at low [Ca²⁺] levels. The real-time CaM-RyR2 binding analysis demonstrated that E46K-CaM had a 10-fold increased RyR2 binding affinity compared with wild-type CaM which may account for the dominant effect of the mutant CaM. Additionally, the E46K-CaM did not affect CaM-Ca²⁺ binding or L-type calcium channel function. Finally, antiarrhythmic agents, nadolol and flecainide, suppressed abnormal Ca²⁺ waves in E46K-cardiomyocytes.

CONCLUSIONS

We, for the first time, established a CaM-related CPVT iPSC-CM model which recapitulated severe arrhythmogenic features resulting from E46K-CaM dominantly binding and facilitating RyR2. In addition, the findings in iPSC-based drug testing will contribute to precision medicine.

Clopidogrel Use in CYP2C19 Loss-of-Function Carriers With High Bleeding Risk After Percutaneous Coronary Intervention

BACKGROUND

It is not known whether clopidogrel use in cytochrome P450 (CYP) 2C19 loss-of-function (LOF) carriers with high bleeding risk (HBR) contributes to adverse outcomes after percutaneous coronary intervention (PCI).Methods and Results: This retrospective observational study included 618 consecutive patients with available CYP2C19 polymorphism information who underwent PCI between September 2014 and August 2021. Patients with HBR (319 [52%] met the Academic Research Consortium definition) were divided into 2 groups according to P2Y₁₂inhibitor action, namely decreased (i.e., clopidogrel in CYP2C19 LOF carriers) and retained (i.e., clopidogrel in CYP2C19 LOF non-carriers or prasugrel regardless of CYP2C19 polymorphisms), and clinical outcomes at 1 year were compared using inverse probability-weighted Cox proportional hazard regression. The primary ischemic outcome (a composite of cardiovascular death, myocardial infarction, or ischemic stroke) was significantly higher in the decreased than retained group (10.2% vs. 3.0%; adjusted hazard ratio [aHR] 2.78; 95% confidence interval [CI] 1.40-5.52; P=0.004). The primary bleeding outcome (Bleeding Academic Research Consortium 3 or 5) did not differ significantly between the decreased and retained groups (3.4% vs. 6.9%, respectively; aHR 0.48; 95% CI 0.22-1.01; P=0.054). There were no interactions between the treatment groups and HBR status in primary ischemic and bleeding outcomes.

CONCLUSIONS

Among patients with HBR, clopidogrel use in CYP2C19 LOF carriers was significantly associated with increased ischemic events after PCI.

Calmodulinopathy is a common cause of critical cardiac phenotypes in fetus and infancy

Background

Cardiac calmodulinopathy is a life-threatening arrhythmia syndrome which presents several phenotypes of inherited primary arrhythmia syndrome (IPAS), and caused by mutations in calmodulin-encoded genes (CALM1–3). We aimed clarify the frequency and their clinical characteristics of calmodulinopathy in our IPAS cohort.

Methods

By using next generation sequencing, we screened arrhythmia related genes including calmodulin-encoding genes in 322 unrelated symptomatic children (0–12 years) who were suspected as IPAS; they included 40 cases with lethal arrhythmic attacks (LAE) under 6-year-old. After gene screening, we investigated their physiological and clinical characteristics about mutation carriers.

Results

Among 322 children, we identified 6 mutations of calmodulin-encoded genes in 9 probands (2.8%); one CALM1 in 2 probands (N98S), and 5 CALM2 in 7 probands (E46K, D96V, D96G, N98S, E141K). Their clinical diagnoses were long QT syndrome (LQTS, n=4), catecholaminergic polymorphic ventricular tachycardia (CPVT, n=3) and both (n=2). Their age of diagnosis ranges at 0–9 with the median of 5 years. There were three major clinical phenotypes; 1) CALM2-D96V, and E141K: two infants with advanced atrio-ventricular block, significant QTc prolongation, severe heart failure from their fetal period – both of them deceased within 1.5-year-old. Their clinical phenotypes resembled classical Timothy syndrome caused by CACNA1C mutations. 2) CALM1-N98S (n=2), CALM2-N98S (n=2), and CALM2-D96G: four preschoolers with LAEs and one syncope: all of them were 3–5 years old. In addition, a T wave morphology of CALM2-D96G carrier was very similar to LQT1. 3) CALM2-E46K (n=2): two were first diagnosed with neurological and developmental disorders, and showed phenotype of CPVT: their cardiac phenotypes were milder compared with that of 1) or 2). Overall, these phenotypes seemed to be mutation specific (indicated in figure). Their cardiac features were severer, and the onset of LAEs was earlier compared with other genotypes of LQTS/CPVT. As the treatment, β-blocker was effective for control of LAEs.

Conclusion

Cardiac calmodulinopathy presented serious and potentially lethal phenotypes in fetus or infancy. To prevent cardiac death in them, we must correctly diagnose and start the treatment as earlier as possible.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): MEXT KAKENHI from the Ministry of Education, Culture, Sports, Science, and Technology of Japan

Adaptive Capon beamforming for lensless electron cyclotron emission imaging with high spatial resolution

Electron cyclotron emission (ECE) imaging diagnostics incorporating a lensless approach have been developed for measurements involving active spatial selectivity and direction-of-arrival estimation. The Capon method for adaptive-array analysis was proposed to improve the spatial resolution of the two-dimensional ECE imaging technique. Broadband noise source emissions were used to simulate the ECE to verify the practical effectiveness of the Capon method in the ECE imaging. Multiple noise source emission positions were properly estimated with a high spatial resolution using the Capon method.

Impact of statin therapy on late target lesion revascularization after everolimus-eluting stent implantation according to pre-interventional vessel remodeling and vessel size of treated lesion

Clinical evidence demonstrating the impact of statins for preventing late target lesion revascularization (TLR) after newer-generation drug-eluting stent implantation and differences in the effect of statins on late TLR according to pre-interventional vessel remodeling and vessel size is limited. We retrospectively evaluated 1193 de novo lesions in 720 patients who underwent everolimus-eluting stent implantation using intravascular ultrasound from January 2010 to December 2012. The primary endpoint was late TLR. Lesions were divided into the statin group (n = 825) and non-statin group (n = 368). The incidence of late TLR was significantly lower in the statin than non-statin group (1.7% vs. 5.2%, respectively; p = 0.001), and within the statin group, it was significantly lower in the follow-up low-density lipoprotein cholesterol (LDL-C) < 100 than ≥ 100 mg/dL level subgroup (1.0% vs. 3.6%, respectively; p = 0.006). Furthermore, in positive remodeling lesions and non-small vessel size lesions, the incidence of late TLR was significantly lower in the statin than non-statin group (1.6% vs. 8.5% and 1.3% vs. 5.3%, respectively; p = 0.001 and p = 0.004). Lowering the LDL-C level using statins was more effective for preventing late TLR after everolimus-eluting stent implantation. Evaluating pre-interventional vessel remodeling patterns and vessel size might be helpful to stratify lesions at high risk of late TLR.

Impact of cascade screening for catecholaminergic polymorphic ventricular tachycardia type 1

Objective

Human cardiac ryanodine receptor 2 (RYR2) shows autosomal-dominant inheritance in catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1); however, de novo variants have been observed in sporadic cases. Here, we investigated CPVT1-related RYR2 variant inheritance and its clinical significance between familial and de novo cases.

Methods

We enrolled 82 independent CPVT1 probands (median age: 10.0 (7.0–13.0) years; 45 male) carrying the RYR2 variants and whose biological origin could be confirmed by parental genetic analysis: assured familial inheritance (familial group: n=24) and de novo variants (de novo group: n=58). We examined the clinical characteristics of the probands and their family members carrying the RYR2 variants.

Results

In the de novo group, the RYR2 variants were more likely located in the C-terminus domain and less likely in the N-terminus domain than those in the familial group. The cumulative incidence of the first cardiac events (syncope and cardiac arrest (CA) or CA only) of the probands at the age of 5 and 10 years was higher in the de novo group than in the familial group. Nearly half of the probands in both groups experienced CA events before diagnosis. Only 37.5% of their genotype-positive parents had symptoms; however, at least 66.7% of the genotype-positive siblings were symptomatic.

Conclusions

CPVT1 probands harbouring de novo RYR2 variants showed an earlier onset of symptoms than those with assured familial inheritance. Cascade screening may enable early diagnosis, risk stratification and prophylactic therapeutic intervention to prevent sudden cardiac death of probands and potential genotype-positive family members.

School-based routine screenings of electrocardiograms for the diagnosis of long QT syndrome

Aims

School-based routine screenings of electrocardiograms (ECGs) have been performed upon admission to primary school (PS), junior high school (JHS), and high school (HS) in Japan. Though ECGs with prolonged QT intervals are occasionally found, the role of regular ECG screening tests in identifying long QT syndrome (LQTS) remains to be determined. We investigated the usefulness of the ECG screenings by comparing the results of genetic tests between students who showed QT-prolongation in the screenings and patients with LQTS.

Methods and results

We genetically screened 341 students (106 PS, 173 JHS, and 62 HS). Of these, 230 subjects showed QT-prolongation during regular screenings (S-S group), and the other 111 patients were clinically consulted with suspected LQTS by paediatricians (C-C group). Genotype–phenotype relationships were compared between the two groups. The positive rates in the genetic tests were comparable among the two groups; however, symptomatic subjects were significantly fewer in the S-S group than the C-C group (3% vs. 70%). Compared to the genotype-negative subjects, the positive subjects showed significantly longer QTc (P &lt; 0.0001) and more frequently presented LQTS risk scores with ≥3.5 points (P &lt; 0.0001). Lethal arrhythmic events (LAE) occurred only in the C-C group; 18 subjects experienced LAE and 83% of them were found to carry variant(s) in the LQTS-related genes.

Conclusion

The school-based ECG screenings are effective in identifying young patients with LQTS who require genetic analysis. If individuals are screened at a younger age, we can identify patients at risk earlier and provide preventative treatments.

Loss-of-function mutations in cardiac ryanodine receptor channel cause various types of arrhythmias including long QT syndrome

AIMS

Gain-of-function mutations in RYR2, encoding the cardiac ryanodine receptor channel (RyR2), cause catecholaminergic polymorphic ventricular tachycardia (CPVT). Whereas, genotype-phenotype correlations of loss-of-function mutations remains unknown, due to a small number of analysed mutations. In this study, we aimed to investigate their genotype-phenotype correlations in patients with loss-of-function RYR2 mutations.

METHODS AND RESULTS

We performed targeted gene sequencing for 710 probands younger than 16-year-old with inherited primary arrhythmia syndromes (IPAS). RYR2 mutations were identified in 63 probands, and 3 probands displayed clinical features different from CPVT. A proband with p.E4146D developed ventricular fibrillation (VF) and QT prolongation whereas that with p.S4168P showed QT prolongation and bradycardia. Another proband with p.S4938F showed short-coupled variant of torsade de pointes (scTdP). To evaluate the functional alterations in these three mutant RyR2s and p.K4594Q previously reported in a long QT syndrome (LQTS), we measured Ca2+ signals in HEK293 cells and HL-1 cardiomyocytes as well as Ca2+-dependent [3H]ryanodine binding. All mutant RyR2s demonstrated a reduced Ca2+ release, an increased endoplasmic reticulum Ca2+, and a reduced [3H]ryanodine binding, indicating loss-of-functions. In HL-1 cells, the exogenous expression of S4168P and K4594Q reduced amplitude of Ca2+ transients without inducing Ca2+ waves, whereas that of E4146D and S4938F evoked frequent localized Ca2+ waves.

CONCLUSION

Loss-of-function RYR2 mutations may be implicated in various types of arrhythmias including LQTS, VF, and scTdP, depending on alteration of the channel activity. Search of RYR2 mutations in IPAS patients clinically different from CPVT will be a useful strategy to effectively discover loss-of-function RYR2 mutations.

Early onset of heart failure in Japanese ARVC patients with pathogenic desmosomal gene variants

Background

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy mainly caused by desmosomal gene variants. Although there are a lot of reports regarding to European ARVC patients, the ones in Asian are a few, and the characteristics of Asian ARVC have been still unclear. We have reported that the genetic backgrounds in Japanese ARVC patients were different from those in European ones. In this study, we aimed to examine the phenotype and outcome of Japanese ARVC patients with specific genetic backgrounds.

Methods and results

This study included 104 Japanese ARVC patients who were diagnosed as definite in the 2010 Task Force Criteria for ARVC and received genetic analysis (79 males [76%]; median age at diagnosis, 40 years [IQR 22–53 years].) Fifty-seven patients carried variants in desmosomal genes classified as pathogenic based on ACMG guideline: 30 in DSG2 (29%), 22 in PKP2 (21%), 2 in DSC2 (2%) and 3 in DSP (3%). The median age of diagnosis was significantly younger in the patients with the pathogenic variants than in those without (37 years [IQR 21–49 years] vs. 46 years [IQR 34–58 years], P=0.01). During a median follow-up of 9.3 years (IQR 3.5–20.9 years), 10 patients died and 2 were received heart transplantation. Sixty-two suffered lethal arrhythmic events including cardiopulmonary arrest, ventricular fibrillation, sustained ventricular tachycardia and appropriate shocks by implantable cardioverter defibrillator. Twenty-two were hospitalized for heart failure. There was no difference in these events rate between the two groups. However, survival analysis revealed that patients with pathogenic variants hospitalized for heart failure significantly earlier in their life than those without (P=0.04, log-rank test, Figure 1).

Conclusions

The Japanese ARVC patients with pathogenic variants in desmosomal genes are diagnosed and hospitalize for heart failure at younger age than those without. These findings have not been reported in other ethnics. Our study warns that we should be cautious for not only the prevention of lethal arrhythmic events but also the progress of the heart failure in Japanese ARVC patients with pathogenic variants.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Japan Agency for Medical Research and Development Figure 1

LMNA Missense Mutation Causes Nonsense-Mediated mRNA Decay and Severe Dilated Cardiomyopathy

BACKGROUND

LMNA is a known causative gene of dilated cardiomyopathy and familial conduction disturbance. Nonsense-mediated mRNA decay, normally caused by nonsense mutations, is a safeguard process to protect cells from deleterious effects of inappropriate proteins from mutated genes. Nonsense-mediated mRNA decay induced by nonstop codon mutations is rare. We investigated the effect of an LMNA missense mutation identified in 2 families affected by cardiac laminopathy.

METHODS

Genomic DNA and total RNA were isolated from patients' peripheral blood lymphocytes or cardiac tissue. LMNA-coding exons were screened by direct sequencing. Complementary DNAs were generated by a reverse transcription-polymerase chain reaction from total RNA. Quantitative polymerase chain reaction was performed to quantify the LMNA complementary DNA amount by using specific primers for lamins A and C. A minigene splicing reporter experiment was performed to assess the effect of detected variants on RNA splicing. The protein expressions of both isoforms were analyzed by Western blotting.

RESULTS

We detected a missense variant c.936 G>C (p. Q312H) at the end of exon 5 of LMNA by genomic DNA sequencing in 2 unrelated families affected by dilated cardiomyopathy and cardiac conduction disturbance. This variant was previously reported in a French family suffering from muscular dystrophy and cardiac conduction disturbance. Sequencing of complementary DNA demonstrated that the mutated allele was absent. By quantitative polymerase chain reaction assay, we confirmed a 90% reduction in LMNA complementary DNA. The minigene splicing reporter assay demonstrated a splicing error by the variant. Western blot analysis revealed that lamin A and C expressions were reduced far >50%.

CONCLUSIONS

We report an LMNA missense mutation found in 2 families, which disrupted a normal splicing site, led to nonsense-mediated mRNA decay, and resulted in severe cardiac laminopathy.

Comparison Between Clopidogrel and Prasugrel Associated With CYP2C19 Genotypes in Patients Receiving Percutaneous Coronary Intervention in a Japanese Population

BACKGROUND

The association between cytochrome P450 (CYP) 2C19 genotypes and adverse events in patients treated with clopidogrel or prasugrel after percutaneous coronary intervention (PCI) in the Japanese population is unclear.Methods and Results:This study consisted of 1,580 patients whoseCYP2C19genotypes were assessed at Shiga University of Medical Science Hospital, and 193 clopidogrel-treated and 217 prasugrel-treated patients who were followed more than 1 year after receiving PCI were analyzed. Among 1,580 patients, the prevalence of normal, intermediate, and poor metabolizers was 32%, 49%, and 17%, respectively. Overall incidence of the primary outcome, defined as a composite of cardiovascular death, myocardial infarction, definite stent thrombosis, ischemic stroke, or major bleeding was not significantly different between the clopidogrel and prasugrel groups (adjusted hazard ratio [HR] 1.98, 95% confidence interval [CI] 0.85-4.61, P=0.12). Among patients with theCYP2C19loss-of-function (LOF) allele, however, the incidence of the primary outcome was significantly higher in the clopidogrel group (adjusted HR 3.19, 95% CI 1.10-9.24, P=0.03), whereas no difference was observed among patients without theCYP2C19LOF allele (adjusted HR 0.67, 95% CI 0.14-3.26, P=0.62).

CONCLUSIONS

Among patients with theCYP2C19LOF allele, the use of clopidogrel was significantly associated with increased adverse events. Thus, further investigation is needed to establish the practical use ofCYP2C19genotyping.

An NGS-based genotyping in LQTS; minor genes are no longer minor

Mutations in KCNQ1, KCNH2, and SCN5A are the major cause of long QT syndrome (LQTS). More than 90% of the genotyped patients have been reported to carry mutations in any of these three genes. Thanks to increasing popularity of next generation sequencer (NGS), novel CACNA1C mutations have been identified among LQTS patients without extra-cardiac phenotypes. We aimed to clarify the frequency of genotypes in LQTS patients in the era of NGS. The study comprised 160 congenital LQTS patients (71 males) registered from November 2015 to September 2018. Inclusion criteria was QTc > 460 ms and Schwartz score ≥ 3. We performed genetic analysis using target gene method by NGS and confirmed the mutations by Sanger method. The median age for genetic screening was 13 (0-68) years. Sixteen patients suffered cardiac arrest, 47 syncope, and 97 were asymptomatic. We identified genetic mutations in 111 (69.4%) patients including 6 CACNA1C (5.4% of the genotyped patients) with 4 asymptomatic patients. Five (3.1%) patients carried double mutations; three out of them with RYR2 and KCNQ1 or KCNH2. In conclusion, CACNA1C screening would be recommended even if the patient is asymptomatic to elucidate the genetic background of the LQTS patients.

High Prevalence of Late-Appearing T-Wave in Patients With Long QT Syndrome Type 8

BACKGROUND

Long QT syndrome type 8 (LQT8) is a rare genotype of long QT syndrome. Late-appearing T-waves (LaT) are often documented in patients with LQT8, as in long QT syndrome type 3 (LQT3); however, the frequency of LaT and its relevance to the clinical severity of LQT8 remains unclear. This study investigated T-wave morphology (TWM) in LQT3 and LQT8 patients and compared the phenotypes of different TWMs.Methods and Results:TWMs were classified into 3 types: early onset T-waves (EoT), LaT, and bifid T-waves (biT). Electrocardiogram (ECG) measurements, symptoms, and topology were compared among TWM types. The study cohort comprised 25 patients with LQT8 (14 mutations) and 25 patients with LQT3 (14 mutations). LaT was detected in 17 (68%) and 13 (52%) LQT8 and LQT3 patients, respectively. There were no significant differences in ECG measurements or the severity of symptoms between patients with LaT and those with other TWMs in either the LQT8 or LQT3 group. However, only patients with LaT experienced cardiopulmonary arrest. Compared with the LQT3 group, in the LQT8 group there was a tendency for mutations in patients with LaT to be located in domain-linking regions.

CONCLUSIONS

In this study, two-thirds of patients with LQT8 exhibited LaT on ECG, and nearly one-third of those experienced cardiopulmonary arrest. Further investigations are warranted to differentiate between LQT3 and LQT8 in patients exhibiting LaT to optimize therapy.

P2865Mutation specific clinical characteristics in long QT syndrome type 8; severe phenotype in Timothy syndrome patients

Background

Long QT syndrome type 8 (LQT8) caused by mutations in CACNA1C has been classified as a very rare and severe type of long QT syndrome accompanied with Timothy syndrome (TS) with extra-cardiac phenotype. Recently, various mutations in CACNA1C have been identified in non-TS patients. However, mutation specific severity in LQT8 has not been elucidated yet, especially for non-TS patients.

Purpose

We aimed to clarify the clinical characteristics of LQT8 patients.

Methods

The study consists of 26 LQT8 patients (21 probands and 5 family members). We evaluated their phenotype.

Results

Table summarizes the clinical characteristics of LQT8 patients. TS patients diagnosed in younger age than those of non-TS. Four TS and one non-TS patients were diagnosed at the age of 0, though the non-TS patient was a son of a patient and asymptomatic. Nine patients suffered symptoms including 7 with cardiac arrest. We identified three TS mutations; classical p.G406R in two and p.G402S in two, and a new TS mutation, p.412M in one. Four of TS patients were symptomatic and two died suddenly at the age of 4 and 5. In contrast, no one died in non-TS patients. Five non-TS patients suffered symptoms in the age of 4,9,15,54 and 64, and the mutations were p.S643F, p.R858H (2 patients), p.K1518E and p.K1591T.

Characteristics of TS and non-TS patient TS Non-TS P N (male) 5 (2) 21 (9) Age (range) 0 (0–7) 12 (0–64) 0.004 Symptom Syncope 4 5 0.034 CPA 3 4 0.101 ECG characteristics   QT interval 603±40 507±14 0.011   T wave alternans 5 2 <0.001   AV Block 4 1 0.002 Therapy (4 unknown)   Beta-blocker 4 7 0.311   Mexiletine 3 1 0.024   ICD implantation 2 2 0.21

Conclusions

Although TS patients showed severe phenotype, most of the non-TS patients were asymptomatic. The phenotype in LQT8 are diversely different depend on the mutations, especially between patients with TS and non-TS.

Novel intracellular transport-refractory mutations in KCNH2 identified in patients with symptomatic long QT syndrome

BACKGROUND

Missense mutations in KCNH2, a gene encoding the Kv11.1 channel, cause long QT syndrome (LQTS) type 2 primarily by disrupting the intracellular transport of Kv11.1 to the plasma membrane. The present study aimed to clarify the functional changes by two novel KCNH2 missense mutations.

METHODS

We performed genetic screening of three unrelated symptomatic LQTS probands with family histories of cardiac symptoms. Chinese hamster ovary cells were transfected with wild-type (WT) and/or mutant KCNH2 plasmid and examined by patch-clamp technique. Immunostaining and confocal microscopy were performed to evaluate the intracellular localization of WT and homozygous mutant Kv11.1 in human embryonic kidney cells. For the study of trafficking rescue, we used low-temperature incubation (30°C). We also examined pharmacological rescue of homozygous mutant Kv11.1 current in cells treated with E-4031 or dofetilide.

RESULTS

We identified two novel KCNH2 missense mutations, G785D and T826I. Electrophysiological study showed that both mutant channels were nonfunctional in homozygous condition and reduced current densities by half in heterozygous condition compared with WT Kv11.1. Heterozygous Kv11.1-G785D produced a significant positive shift in activation and a significant negative shift in inactivation, whereas heterozygous Kv11.1-T826I caused no kinetic changes. Immunostaining revealed that both were transport-refractory mutations. Incubation at 30°C rescued plasma membrane expression of Kv11.1-T826I but not G785D. We confirmed low-temperature-induced restoration of homozygous Kv11.1-T826I transport by functional current measurements. In contrast, incubation with E-4031 or dofetilide failed to produce measurable currents in both homozygous mutant channels.

CONCLUSIONS

Two novel KCNH2 mutations disrupted the intracellular transport of Kv11.1. Low-temperature incubation rescued plasma membrane expression of Kv11.1-T826I but not G785D. Both mutations exerted loss-of-function effects on Kv11.1 and explained the phenotypes of the mutation carriers.

Phenotypic Variability of ANK2 Mutations in Patients With Inherited Primary Arrhythmia Syndromes

BACKGROUND

Mutations inANK2have been reported to cause various arrhythmia phenotypes. The prevalence ofANK2mutation carriers in inherited primary arrhythmia syndrome (IPAS), however, remains unknown in Japanese. Using a next-generation sequencer, we aimed to identifyANK2mutations in our cohort of IPAS patients, in whom conventional Sanger sequencing failed to identify pathogenic mutations in major causative genes, and to assess the clinical characteristics ofANK2mutation carriers.Methods and Results:We screened 535 probands with IPAS and analyzed 46 genes including wholeANK2exons using a bench-top NGS (MiSeq, Illumina) or performed whole-exome-sequencing using HiSeq2000 (Illumina). As a result, 12 of 535 probands (2.2%, aged 0-61 years, 5 males) were found to carry 7 different heterozygousANK2mutations.ANK2-W1535R was identified in 5 LQTS patients and 1 symptomatic BrS and was predicted as damaging by multiple prediction software. In total, as to phenotype, there were 8 LQTS, 2 BrS, 1 IVF, and 1 SSS/AF. Surprisingly, 4/8 LQTS patients had the acquired type of LQTS (aLQTS) and suffered torsades de pointes. A total of 7 of 12 patients had documented malignant ventricular tachyarrhythmias.

CONCLUSIONS

VariousANK2mutations are associated with a wide range of phenotypes, including aLQTS, especially with ventricular fibrillation, representing "ankyrin-B" syndrome. (Circ J 2016; 80: 2435-2442).

Multigenerational Inheritance of Long QT Syndrome Type 2 in a Japanese Family

Congenital long QT syndrome (LQTS) is an important cause of sudden cardiac death in young people without any other structural disease. Mutations in the genes encoding the cardiac ion channels or associated proteins have been shown to result in ion channel dysfunction and thereby causing LQTS. We investigated a Japanese family with LQTS for four generations, with the female family members showing severe symptoms. We performed genetic tests for LQTS-related genes and identified a heterozygous KCNH2 mutation (p.K638del). In the family, the KCNH2 mutation had a very high multigenerational inheritance, and female genotype positives showed more severe phenotypes.

Novel SCN10A variants associated with Brugada syndrome

AIMS

The expression of sodium channel Nav1.8 in cardiac nervous systems has been identified, and variants of SCN10A that encodes Nav1.8 contribute to the development of Brugada syndrome (BrS) by modifying the function of Nav1.5 or directly reducing the sodium current. The aim of this study was to identify the frequency of SCN10A mutations in Japanese patients with BrS and to compare the phenotypical differences between patients with BrS and those who have other BrS-causative genes.

METHODS AND RESULTS

This study involved 240 Japanese probands who were clinically suspected with BrS and were negative for mutations in major BrS-related genes. We screened for the SCN10A gene using a high-resolution melting method and direct sequencing. In addition, we compared the clinical characteristics among the probands with gene mutations in SCN10A, 6 probands with CACNA1C and 17 probands with SCN5A. We identified six SCN10A variant carriers (2.5%): W189R, R844H (in two unrelated probands), N1328K, R1380Q, and R1863Q. Five were male. Four were symptomatic: one died following sudden cardiopulmonary arrest at age 35, one suffered ventricular fibrillation, and two had recurrent syncope. Compared with BrS patients carrying SCN5A or CACNA1C mutations, although there were no significant differences among them, symptomatic patients in the SCN10A group tended to be older than those in the other gene groups.

CONCLUSION

In six BrS probands who carried SCN10A variants, most experienced severe arrhythmic attacks. It is of clinical importance to screen SCN10A mutations in BrS, although the functional significance of these variants remains unclear.

Long QT syndrome type 8: novel CACNA1C mutations causing QT prolongation and variant phenotypes

AIMS

CACNA1C mutations have been reported to cause LQTS type 8 (LQT8; Timothy syndrome), which exhibits severe phenotypes, although the frequency of patients with LQT8 exhibiting only QT prolongation is unknown. This study aimed to elucidate the frequency of CACNA1C mutations in patients with long QT syndrome (LQTS), except those with Timothy syndrome and investigate phenotypic variants.

METHODS AND RESULTS

CACNA1C gene screening was performed in 278 probands negative for LQTS-related gene mutations. Functional analysis of mutant channels using a whole-cell patch-clamp technique was also performed. Using genetic screening, we identified five novel CACNA1C mutations: P381S, M456I, A582D, R858H, and G1783C in seven (2.5%) unrelated probands. Seven mutation carriers showed alternative clinical phenotypes. Biophysical assay of CACNA1C mutations revealed that the peak calcium currents were significantly larger in R858H mutant channels than those of wild-type (WT). In contrast, A582D mutant channels displayed significantly slower inactivation compared with WT. The two mutant channels exerted different gain-of-function effects on calcium currents.

CONCLUSION

In patients with LQTS, the frequency of CACNA1C mutations was higher than reported. Even without typical phenotypes of Timothy syndrome, CACNA1C mutations may cause QT prolongation and/or fatal arrhythmia attacks.

Gain-of-function KCNH2 mutations in patients with Brugada syndrome

BACKGROUND

Brugada syndrome (BrS) is an inherited disease characterized by right precordial ST segment elevation on electrocardiograms (ECGs) that predisposes patients to sudden cardiac death as a result of polymorphic ventricular tachyarrhythmia or ventricular fibrillation (VF). In BrS patients, except for SCN5A, mutations in other responsible genes are poorly elucidated.

METHODS AND RESULTS

We identified 4 KCNH2 mutations, T152I, R164C, W927G, and R1135H, in 236 consecutive probands with BrS or Brugada-like ECG. Three of these mutation carriers showed QTc intervals shorter than 360 milliseconds and 1 experienced VF. We performed patch-clamp analyses on I(Kr) reconstituted with the KCNH2 mutations in Chinese hamster ovary cells and compared the phenotypes of the patients with different genotypes. Three mutations, R164C, W927G, and R1135H, increased I(Kr) densities. Three mutations, T152I, R164C, and W927G, caused a negative shift in voltage-dependent activation curves. Only the R1135H mutant channel prolonged the deactivation time constants. We also identified 20 SCN5A and 5 CACNA1C mutation carriers in our cohort. Comparison of probands' phenotypes with 3 different genotypes revealed that KCNH2 mutation carriers showed shorter QTc intervals and SCN5A mutation carriers had longer QRS durations.

CONCLUSIONS

All KCNH2 mutations that we identified in probands with BrS exerted gain-of-function effects on I(Kr) channels, which may partially explain the ECG findings in our patients.

Nonsense-mediated mRNA decay due to a CACNA1C splicing mutation in a patient with Brugada syndrome

BACKGROUND

Brugada syndrome (BrS) is an inherited cardiac arrhythmia associated with sudden death due to ventricular fibrillation. Mutations in genes related to the cardiac L-type calcium channel have been reported to be causative of BrS. Generally, the messenger RNA (mRNA) that contains a nonsense mutation is rapidly degraded via its decay pathway, which is known as nonsense-mediated mRNA decay (NMD). Previously, we reported a male patient with BrS who carried c.1896G>A (the first nucleotide of CACNA1C exon 14), which caused a synonymous mutation, p.R632R.

OBJECTIVE

To examine how the synonymous CACNA1C mutation p.R632R produces the phenotype of BrS, with a special emphasis on the splicing error and NMD processes.

METHODS

We extracted mRNA from leukocytes of the proband and his 2 children and performed reverse transcription polymerase chain reaction. Complementary DNAs were checked by using direct sequencing and quantitative analysis.

RESULTS

The subsequent sequence electropherogram of the complementary DNAs did not show the substitution of the nucleotide identified in the genomic DNA of the proband. In the mRNA quantification analysis, we confirmed that reduction in the CACNA1C expression level was suspected to be caused by NMD.

CONCLUSIONS

Mutant mRNA with a c.1896G>A substitution may be diminished by NMD, and the resultant decrease in CACNA1C message leads to a novel mechanism for inducing BrS that is distinct from that reported previously.

Age-dependent clinical and genetic characteristics in Japanese patients with arrhythmogenic right ventricular cardiomyopathy/dysplasia

BACKGROUND

 Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a heart muscle disease caused by desmosomal gene mutations, and presents as ventricular tachycardia and sudden cardiac death. Although the mean age at onset or diagnosis of ARVC/D are reported to be around the 30-40s, the age-dependent clinical and genetic differences remain unknown.

METHODS AND RESULTS

 A total of 35 consecutive Japanese probands (23 male) who were clinically diagnosed with ARVC/D were enrolled in the present study, and genetic analysis of PKP2, DSP, DSG2, and DSC2 was done. The mean age at the first symptom and at diagnosis was 38.6±14.8 years and 40.5±17.7 years, respectively. Probands in whom the onset was cardiopulmonary arrest were significantly younger (22.3±15.3 years) than those with arrhythmia (41.1±13.2 years) or congestive heart failure (45.7±8.5 years). On genetic screening, 19 mutation carriers were identified. Although there was no age dependence for each gene mutation carrier, carriers with PKP2 premature stop codon developed the disease at a significantly younger age than other mutation carriers.

CONCLUSIONS

 The initial clinical manifestations in some young probands were very severe, and PKP2 mutations with a premature stop codon would be associated with disease onset at a younger age. 

An ethical and social examination of dementia as depicted in Japanese film

The ageing population means that dementia is a serious social problem in Japan. Attitudes toward ageing in Japan are increasingly negative, and views of life and death among older people vary. Numerous ethical problems exist in the medical treatment of dementia. Amidst such conditions, it is important and beneficial to examine films that depict demented patients and to consider the issues raised by these films. Through film we see many aspects of a country and its times: culture and ideology, morality and religion, medical treatments, views on life and death, social conditions and what issues are viewed as problems. The best films both entertain audiences and provide viewers with opportunities to think about social problems. In the past 30 years, 10 films about dementia had been made in Japan and two of these-The Twilight Years (Kôkotsu no hito) and Memories of Tomorrow (Ashita no kioku) are the main focus of this paper. In our analysis we consider three points: how the patients are informed of their disease, the characters' wishes for death, and terminal medical care.

A report on small team clinical ethics consultation programmes in Japan

Clinical ethics support, including ethics consultation, has become established in the field of medical practice throughout the world. This practice has been regarded as useful, most notably in the UK and the USA, in solving ethical problems encountered by both medical practitioners and those who receive medical treatment. In Japan, however, few services are available to respond to everyday clinical ethical issues, although a variety of difficult ethical problems arise daily in the medical field: termination of life support, euthanasia and questions about patient autonomy. In light of these conditions, a group of 17 volunteer educators and researchers from the area of biomedical ethics, including the authors, have formed the Clinical Ethics Support and Education Project, and began providing Japan's first small team clinical ethics consultation service in October, 2006. Members include scholars of biomedical ethics, scholars of philosophy and ethics, legal professionals and legal scholars, nurses and doctors, consisting of five women and 12 men. Consultation teams, made up of a small number of members, were organised each time a request for consultation was received. Over approximately 15 months (October 2006-December 2007), the programme received 22 consultation requests from medical practitioners and medical institutions, and three from the families of patients. In this paper, we will discuss the status of our consultation service and examples of consultation cases we have handled. In addition, we will examine the process of evaluating small team clinical ethics consultation services, as well as the strengths and weakness of such programmes.

Genogrouping of Vaccine Breakdown Strains (VBS) of Feline Calicivirus in Japan

Although prevention of feline calcivirus (FCV) infection by vaccination has been attempted, and isolation of FCV, development of the disease, and a few fatal cases in vaccinated cats have been reported. Fifteen FCV strains isolated from cats that had been vaccinated with commercially available FCV vaccines (F9, FCV-255, and FC-7) were genogrouped. Molecular analysis of viral genomes involved the construction of a phylogenetic tree of capsid genes using the NJ method. Cat anti-F9 serum and rabbit anti-FCV-255 serum were used for virus neutralization tests. Molecular phylogenetic analysis of the amino acid sequences of 15 virus isolates and those of the previously published and GenBank-deposited 9 global and 14 Japanese strains showed that 8 (53%) of the 15 virus isolates as well as the vaccine strains F9 and FCV-255 belonged to genogroup I (G(A)I), and 7 (47%) belonged to genogroup II (G(A)II). Of the 8 G(A)I strains, 2 were isolated from cats that had been vaccinated with an F9 strain live vaccine, 5 from cats vaccinated with an FCV-255-derived vaccine, and 1 from a cat vaccinated with an FC-7-derived vaccine. Of the 7 GAll strains, 5 were isolated from cats that had been vaccinated with the F9 strain live vaccine, 1 from a cat vaccinated with the FCV-255-derived vaccine, and 1 from a cat vaccinated with the FC-7-derived vaccine. These results indicate that more vaccine breakdown strains isolated from the cats vaccinated with the F9 strain-derived vaccine belong to G(A)II than to G(A)I, whereas more vaccine breakdown strains isolated from the cats vaccinated with the FCV-255 strain-derived vaccine belong to G(A)I than to G(A)II, and that when the FC-7 strain-derived vaccine is used, the vaccine breakdown strains belong almost equally to G(A)I and G(A)II. Thus, the genogroups of virus isolates varied with the vaccine strain used (p < 0.05). On the other hand, the neutralizing titres of feline anti-F9 serum and rabbit anti-FCV-255 serum against the 15 isolates were very low, showing no relationships between neutralizing antibody titres and genogroups. The DNA sequence identities between the virus isolates and the vaccine strains were low, at 70.6-82.9%, and no strains were found to have sequences derived from the vaccine strains. Alignment of amino acid sequences showed that the G(A)I or G(A)II virus isolates from the F9-vaccinated cats differed at position 428 of the 5' hypervariable region (HVR) of capsid region of the F9 strain, whereas those from the FCV-255-vaccinated cats differed at positions 438, 453, and 460 of the 5'HVR of capsid region E of the F9 strain. We speculate that these differences influence genogrouping. The amino acid changes within the F9 linear epitopes common to G(A)I and G(A)II were noted at positions 450, 451, 457 of 5'HVR of the capsid region E in the isolates from F9-derived vaccine-treated cats, and 449, 450, and 451 of 5'HVR of capsid region E in the isolates from FCV-255-derived vaccine-treated cats, suggesting that these amino acid changes are involved in escapes. These results suggest that alternate vaccination with the F9 and FCV-255 strains or the use of a polyvalent vaccine containing GAll strains serves to inhibit development.

Detection of Feline calicivirus (FCV) from Vaccinated Cats and Phylogenetic Analysis of its Capsid Genes

We analysed genogroups of four feline calcivirus (FCV) isolates (FCV-S, H10, Ao198-1 and ML89) obtained from cats that experienced FCV infection after having been vaccinated against FCV. New PCR primer sets (8F/8R, Ao-S/Ao-A, cp-S/cp-A) were also designed, since the conventional Seal primer failed to amplify the target sequences in two samples. The genogroups of the four isolates as well as eight global and 17 domestic strains were determined by phylogenetic analysis of their amino acid sequences. One out of the four strains (25%) isolated in this study, H10, was grouped into genogroup I, along with the vaccine strains F9 and FCV-255. The other three isolates (75%) belonged to genogroup II. Thus, there were more isolates in genogroup II than in genogroup I. However, the antibody values of the four isolates against cat anti-F9 antisera were significantly decreased. There may be no relationship between the neutralizing antibody titre and genogroup. Amino acid sequence alignment of the four isolates showed that only a single amino acid in region C, which is involved in neutralization epitopes, was different in ML89 strain from that of F9. The other three strains, H10, Ao198-1 and FCV-B, shared the same amino acid sequence with F9. Alignment of amino acids for linear epitopes in the F9 strain, which are located at regions D and E, showed variations in 5' hypervariable region (HVR) of E, whereas D and conE had only synonymous substitutions i.e. no change in the amino acid sequence. This mutation in 5' HVR of region E suggested a vaccine breakdown, as the region is known to be essential for antigenicity. The genogroup II FCV is likely to be the cause of the FCV infection in this study, while the vaccine strains belong to genogroup I. Thus, the existing vaccine may need reevaluation for its effectiveness.

Capsid protein genetic analysis and viral spread to the spinal cord in cats experimentally infected with feline calicivirus (FCV)

We investigated primitively the molecular basis of the neural spread of a feline calcivirus isolate (FCV-S) from the spinal cord of a cat that died after manifesting excitation. Experimental infections of cats with three clones from parent virus isolate FCV-S, isolated based on plaque size, were performed, and virus recovery from the spinal cord and the nucleotide and predicted amino acid sequences of the viral capsid protein region (ORF2) were compared. In the experimental infection with the one-time cloned virus (C1L1) isolated from a large plaque, the C1L1 was recovered from the spinal cord. In contrast, seven-times cloned C6L7 (from large plaque) and five-times cloned C5S2 (isolated from small plaque) were not recovered from the spinal cord. Genetic analysis of the capsid protein gene of the three viral clones revealed that four bases were different and two amino acids were different at positions 34 (Val in C6L7 and Ala in C1L1 and C5S2) and 46 (Leu in C6L7 and Pro in C1L1 and C5S2) between C6L7 (with large plaque) and C5S2 (with small plaque). The amino acid at position 434 of C1L1 was different from those of C6L7 and C5S2 (Gly in C1L1, D (Asp) in C6L7 and C5S2). From these results, the plaque size seemed not to be related to the spread of virus to the spinal cord. Clone C1L1, which spread to the spinal cord, had a difference of one amino acid from the other two clones, which may be related to the ability to spread to the spinal cord.