Geno- and phenotypic characteristics and clinical outcomes of CACNA1C gene mutation associated Timothy syndrome, "cardiac only" Timothy syndrome and isolated long QT syndrome 8: A systematic review.

Background: Mutations in the CACNA1C gene-encoding for the major Ca2+ channel of the heart-may exhibit a variety of clinical manifestations. These include typical or atypical Timothy syndromes (TS) which are associated with multiple organ manifestations, and cardiac involvement in form of malignant arrhythmias, QTc prolongation, or AV block. "Cardiac only" Timothy syndrome (COTS) shows no extracardiac manifestation, whereas some CACNA1C gene mutations are associated with QTc prolongation alone (isolated long QT syndrome 8, LQT8). Methods: A systematic search of the literature reporting cases of CACNA1C gene mutation associated syndromes, including TS, COTS and isolated LQT8 via major databases published from 2004 through 2019 was performed. Detailed patient-level phenotypic and genotypic characteristics, as well as long-term outcome measures were collected and compared between pre-specified patient groups, defined both on phenotype and genotype. Results: A total of 59 TS, 6 COTS, and 20 isolated LQT8 index cases were identified. Apart of syndactyly or baldness, there were no major differences regarding clinical manifestations or outcome measures between TS subtypes, either defining TS subtypes on the genotype or based on the phenotype. Both subtypes were characterized by an extreme degree of QTc prolongation (median ≥600 ms) which were reflected in high major adverse cardiac event rate. On the other hand, there were marked differences between TS, COTS, and isolated LQT8. Timothy syndrome was characterized by a much earlier disease onset, much more pronounced QTc prolongation and much higher mortality rate than COTS or isolated LQT8. Similar differences were observed comparing CACNA1C exon 8/8A vs. non-exon 8/8A mutation carriers. TS showed a high degree of genetic homogeneity, as the p.Gly406Arg mutation either in exon 8 or exon 8A alone was responsible for 70% of the cases. Conclusions: Clinical phenotypes associated with mutations in the CACNA1C gene show important clinical differences. Timothy syndrome is associated with the most severe clinical phenotype and with the highest risk of morbidity and mortality. However, distinguishing TS subtypes, in any form, are not supported by our data. Systematic review registration: [https://www.crd.york.ac.uk/prospero/], identifier [CRD42020184737].

The Genetic Architecture of Hypertrophic Cardiomyopathy in Hungary: Analysis of 242 Patients with a Panel of 98 Genes.

Hypertrophic cardiomyopathy (HCM) is a primary disease of the myocardium most commonly caused by mutations in sarcomeric genes. We aimed to perform a nationwide large-scale genetic analysis of a previously unreported, representative HCM cohort in Hungary. A total of 242 consecutive HCM index patients (127 men, 44 ± 11 years) were studied with next generation sequencing using a custom-designed gene-panel comprising 98 cardiomyopathy-related genes. A total of 90 patients (37%) carried pathogenic/likely pathogenic (P/LP) variants. The percentage of patients with P/LP variants in genes with definitive evidence for HCM association was 93%. Most of the patients with P/LP variants had mutations in MYBPC3 (55 pts, 61%) and in MYH7 (21 pts, 23%). Double P/LP variants were present in four patients (1.7%). P/LP variants in other genes could be detected in ≤3% of patients. Of the patients without P/LP variants, 46 patients (19%) carried a variant of unknown significance. Non-HCM P/LP variants were identified in six patients (2.5%), with two in RAF1 (p.Leu633Val, p.Ser257Leu) and one in DES (p.Arg406Trp), FHL1 (p.Glu96Ter), TTN (p.Lys23480fs), and in the mitochondrial genome (m.3243A>G). Frameshift, nonsense, and splice-variants made up 82% of all P/LP MYBPC3 variants. In all the other genes, missense mutations were the dominant form of variants. The MYBPC3 p.Gln1233Ter, the MYBPC3 p.Pro955ArgfsTer95, and the MYBPC3 p.Ser593ProfsTer11 variants were identified in 12, 7, and 13 patients, respectively. These three variants made up 36% of all patients with identified P/LP variants, raising the possibility of a possible founder effect for these mutations. Similar to other HCM populations, the MYBPC3 and the MYH7 genes seemed to be the most frequently affected genes in Hungarian HCM patients. The high prevalence of three MYBPC3 mutations raises the possibility of a founder effect in our HCM cohort.

Variant Transthyretin Amyloidosis (ATTRv) in Hungary: First Data on Epidemiology and Clinical Features.

BACKGROUND: Variant transthyretin amyloidosis (ATTRv) is an autosomal dominant inherited disease, where the mutation of the transthyretin gene (TTR) results in the deposition of pathogenic protein fibrils in various tissues. The mutation type influences the clinical course. Until now, no data were available on the genotype, phenotype, and prevalence of Hungarian ATTRv patients. The aim of our study was to assess the prevalence, regional distribution, genotypes, and phenotypes of Hungarian patients with ATTRv. METHODS: With the collaboration of Hungarian regional and university centers, we identified patients diagnosed with ATTRv. We also searched prior publications for case studies of Hungarian ATTRv patients. RESULTS: 40 individuals in 23 families with ATTRv were identified within the borders of Hungary. At the time of the diagnosis, 24 of them were symptomatic. The two most common mutations were ATTRHis88Arg (nine families) and ATTRIle107Val (8 families). ATTRVal30Met was demonstrated in 2 families, and ATTRVal122del, ATTRPhe33Leu, ATTRIle84Ser, and ATTRAsp18Gly in one family each. The median age of the symptomatic patients at the time of clinical diagnosis was 65 years. The most common clinically significant organ involvement was restrictive cardiomyopathy, found in 24 patients. Polyneuropathy was diagnosed in 20 patients. A total of 19 patients showed a mixed phenotype. The leading symptom was heart failure in 8 cases (3 of them had only cardiac symptoms), polyneuropathy in 11 cases (all of them also had cardiac symptoms), and equally severe cardiac and neuropathy symptoms were present in 3 cases. Out of 24 symptomatic patients, 10 received targeted pharmacological therapy. The follow-up period ranged from 1 to 195 months. At the time of the retrospective analysis, 12 patients had already died, and 1 patient underwent heart transplantation. CONCLUSIONS: As TTR genotype influences the phenotype and clinical course of ATTRv, it is important to know the regional data. In Hungary, ATTRHis88Arg and ATTRIle107Val are the most common mutations in ATTRv, both presenting with mixed phenotype, but the median age at the time of the diagnosis is 9 years lower in patients with ATTRHis88Arg than in patients with ATTRIle107Val.

Impaired cytoplasmic domain interactions cause co-assembly defect and loss of function in the p.Glu293Lys KNCJ2 variant isolated from an Andersen-Tawil syndrome patient.

AIMS: Subunit interactions at the cytoplasmic domain interface (CD-I) have recently been shown to control gating in inward rectifier potassium channels. Here we report the novel KCNJ2 variant p.Glu293Lys that has been found in a patient with Andersen-Tawil syndrome type 1 (ATS1), causing amino acid substitution at the CD-I of the inward rectifier potassium channel subunit Kir2.1. Neither has the role of Glu293 in gating control been investigated nor has a pathogenic variant been described at this position. This study aimed to assess the involvement of Glu293 in CD-I subunit interactions and to establish the pathogenic role of the p.Glu293Lys variant in ATS1. METHODS AND RESULTS: The p.Glu293Lys variant produced no current in homomeric form and showed dominant-negative effect over wild-type (WT) subunits. Immunocytochemical labelling showed the p.Glu293Lys subunits to distribute in the subsarcolemmal space. Salt bridge prediction indicated the presence of an intersubunit salt bridge network at the CD-I of Kir2.1, with the involvement of Glu293. Subunit interactions were studied by the NanoLuc® Binary Technology (NanoBiT) split reporter assay. Reporter constructs carrying NanoBiT tags on the intracellular termini produced no bioluminescent signal above background with the p.Glu293Lys variant in homomeric configuration and significantly reduced signals in cells co-expressing WT and p.Glu293Lys subunits simultaneously. Extracellularly presented reporter tags, however, generated comparable bioluminescent signals with heteromeric WT and p.Glu293Lys subunits and with homomeric WT channels. CONCLUSIONS: Loss of function and dominant-negative effect confirm the causative role of p.Glu293Lys in ATS1. Co-assembly of Kir2.1 subunits is impaired in homomeric channels consisting of p.Glu293Lys subunits and is partially rescued in heteromeric complexes of WT and p.Glu293Lys Kir2.1 variants. These data point to an important role of Glu293 in mediating subunit assembly, as well as in gating of Kir2.1 channels.

Direct Anticoagulants and Risk of Myocardial Infarction, a Multiple Treatment Network Meta-Analysis.

We assessed the cardiovascular safety of long-term direct-acting oral anticoagulant (DOAC) treatment. A search of the medical literature was performed from inception until May 31, 2019. Inclusion criteria were (1) randomized trial that assessed the clinical efficacy and/or safety of 1 or more DOAC, (2) control group including oral anticoagulation and/or antiplatelet and/or placebo treatment, and (3) the incidence of acute coronary syndrome during follow-up was reported. Fixed-effect and random-effects models were applied. The analyzed outcomes were myocardial infarction (MI), major bleeding, and mortality. Twenty-eight randomized clinical trials (196 761 patients) were included. Rivaroxaban was associated with a 21% reduction in the relative risk of MI when compared to placebo (relative risk [RR]: 0.79 [95% credible interval, CrI: 0.65-0.94]) and a 31% reduction (RR: 0.70 [95% CrI: 0.53-0.89]) when compared to dabigatran. Apixaban resulted in 24% (RR: 0.76 [95% CrI: 0.58-0.99]) and vitamin K antagonists anticoagulation resulted in 19% (RR: 0.81 [95% CrI: 0.65-0.98]) risk reduction compared to dabigatran. The computed probability of being the first best choice of treatment was 61.8% for rivaroxaban. Cardiovascular safety shows considerable heterogeneity among oral anticoagulants. Treatment with rivaroxaban is associated with reduced rate of MI.

A novel 'splice site' HCN4 Gene mutation, c.1737+1 G>T, causes familial bradycardia, reduced heart rate response, impaired chronotropic competence and increased short-term heart rate variability.

BACKGROUND: The most important molecular determinant of heart rate regulation in sino-atrial pacemaker cells includes hyperpolarization-activated, cyclic nucleotide-gated ion channels, the major isoform of which is encoded by the HCN4 gene. Mutations affecting the HCN4 gene are associated primarily with sick sinus syndrome. METHODS AND RESULTS: A novel c.1737+1 G>T 'splice-site' HCN4 mutation was identified in a large family with familial bradycardia which co-segregated with the disease providing a two-point LOD score of 4.87. Twelve out of the 22 investigated family members [4 males, 8 females average age 36 (SD 6) years] were considered as clinically affected (heart rate<60/min on resting ECG). Minimum [36 (SD 7) vs. 47 (SD 5) bpm, p=0.0087) and average heart rates [62 (SD 8) vs. 73 (SD 8) bpm, p=0.0168) were significantly lower in carriers on 24-hour Holter recordings. Under maximum exercise test carriers achieved significantly lower heart rates than non-carrier family members, and percent heart rate reserve and percent corrected heart rate reserve were significantly lower in carriers. Applying rigorous criteria for chronotropic incompetence a higher number of carriers exhibited chronotropic incompetence. Parameters, characterizing short-term variability of heart rate (i.e. rMSSD and pNN50%) were increased in carrier family members, even after normalization for heart rate, in the 24-hour ECG recordings with the same relative increase in 5-minute recordings. CONCLUSIONS: The identified novel 'splice site' HCN4 gene mutation, c.1737+1 G>T, causes familial bradycardia and leads to reduced heart rate response, impaired chronotropic competence and increased short-term heart rate variability in the mutation carriers.

Identification of a Novel GLA Gene Mutation, p.Ile239Met, in Fabry Disease With a Predominant Cardiac Phenotype.

Fabry disease (FD) is an X-linked inherited lysosomal storage disorder caused by mutations in the GLA gene, encoding for the enzyme α-galactosidase A. Although hundreds of mutations in the GLA gene have been described, many of them are variants of unknown significance. Here we report a novel GLA mutation, p.Ile239Met, identified in a large Hungarian three-generation family with FD. A 69 year-old female index patient with a clinical history of renal failure, hypertrophic cardiomyopathy, and 2nd degree AV block was screened for mutation in the GLA gene. Genetic screening identified a previously unreported heterozygous mutation in exon 5 of the GLA gene (c.717A>G; p.Ile239Met). Family screening indicated that altogether 6 family members carried the mutation (5 females, 1 male, average age: 55 ± 16 years). Three family members, including the index patient, manifested the cardiac phenotype of hypertrophic cardiomyopathy, while two other family members were diagnosed with left ventricular hypertrophy. Taking affection status as the presence of hypertrophic cardiomyopathy, left ventricular hypertrophy or elevated lyso-Gb3 levels, all affected family members carried the mutation. Linkage analysis of the family gave a two-point LOD score of 2.01 between the affection status and the p.Ile239Met GLA mutation. Lyso-Gb3 levels were elevated in all carrier family members (range: 2.4-13.8 ng/mL; upper limit of normal +2STD: ≤ 1.8 ng/mL). The GLA enzyme level was markedly reduced in the affected male family member (< 0.2 µmol/L/hour; upper limit of normal ± 2STD: ≥ 2.6 µmol/L/hour). We conclude that the p. Ile239Met GLA mutation is a pathogenic mutation for FD associated with predominant cardiac phenotype.

Identification of Two Novel LAMP2 Gene Mutations in Danon Disease.

BACKGROUND: Danon disease is a rare X-linked inherited disorder characterized by massive left ventricular hypertrophy, skeletal muscle dystrophy, and mental retardation. The disease is caused by mutations in the LAMP2 gene encoding for lysosome-associated membrane protein-2. METHODS: Two young male patients with hypertrophic cardiomyopathy, characterized by marked, concentric left ventricular hypertrophy, elevated levels of creatine kinase, and manifest limb-girdle muscular dystrophy in 1 case, were investigated. Genetic screening included direct sequencing of the whole coding sequence of the LAMP2 gene. RESULTS: Genetic analysis identified 2 novel LAMP2 gene mutations. In Family A, a G-A transition (c.962G > A) leading to a nonsense mutation at codon 321 (p.Trp321Ter), and in Family B, a one-nucleotide insertion (c.973insC) leading to a full frame-shift (p.Pro324+24X) was detected in exon 8 of the LAMP2 gene. Family screening identified 8 mutation carriers, with 4 nonpenetrant cases and 3 additional, probably affected family members without DNA diagnosis. The cardiac phenotype was hypertrophic cardiomyopathy in all cases, including female mutation carriers. Five disease-related deaths occurred in the families, at an average age of 33 ± 16 years, which was clearly lower in male than in female patients (28 ± 7 vs 42 ± 25 years). A high prevalence of arrhythmias or conduction abnormalities was also observed. CONCLUSIONS: The reported 2 novel LAMP2 gene mutation carrier families, one of them being one of the largest reported to date, highlight the malignant clinical course of Danon disease, characterized by a high rate of disease-related death at an early age and a high prevalence of arrhythmias or conduction abnormalities.