KCNJ2 mutation results in Andersen syndrome with sex-specific cardiac and skeletal muscle phenotypes

A Late Diagnosis of Andersen-Tawil Syndrome in Teenage Siblings

BACKGROUND

Andersen-Tawil syndrome (ATS) is a rare autosomal dominant disorder characterized by a classic symptom triad, including periodic paralysis, ventricular arrhythmias with associated prolonged QT interval and U waves, and dysmorphic facial and skeletal features. Pathogenic variants of the KCNJ2 gene are linked to ATS.

METHODS

We present two siblings with the same pathogenic mutation and facial characteristic of hypotelorism, yet with intrafamilial and sex-specific variability.

RESULTS

The first patient is a 16-year-old male who presented from an outside hospital with subacute-onset weakness. The symptoms almost completely subsided the following day, with only mild proximal muscle weakness. Magnetic resonance imaging of the brain and cervical spine was unremarkable. He had one prior attack of self-resolving weakness without apparent triggering factors and a history of premature ventricular contractions and U waves seen on electrocardiogram without cardiac symptoms. On further evaluation his physical examination was significant for micrognathia, hypotelorism, and clinodactyly. Electrodiagnostic examination showed no clear evidence of polyneuropathy. Given his presentation of the typical triad of periodic weakness, dysmorphic features, and cardiac rhythm abnormalities, genetic testing was pursued revealing a pathogenic mutation of the KCNJ2 gene, indicative of ATS. Subsequent genetic testing of his older biological sister, with identical physical features but without a history of cardiac symptoms or episodic periodic paralysis, revealed the same pathogenic mutation.

CONCLUSIONS

It is essential to note that ATS can manifest with a wide range of symptoms and some individuals may display only subtle or atypical signs, contributing to this challenging diagnosis.

Management of ultrarare inherited arrhythmia syndromes

Ultrarare inherited arrhythmia syndromes are increasingly diagnosed as a result of increased awareness as well as increased availability and reduced cost of genetic testing. Yet by definition, their rarity and heterogeneous expression make development of evidence-based management strategies more challenging, typically employing strategies garnered from similar genetic cardiac disorders. For the most part, reliance on anecdotal experiences, expert opinion, and small retrospective cohort studies is the only means to diagnose and to treat these patients. Here we review the management of specific ultrarare inherited arrhythmic syndromes together with the genetic and molecular basis, which will become increasingly important with the development of targeted therapies to correct the biologic basis of these disorders.

From Bedside to Bench and Back: Advancing Our Understanding of the Pathophysiology of Cleft Palate and Implications for the Future

OBJECTIVE

To provide a comprehensive understanding of the pathophysiology of cleft palate (CP) and future perspectives.

DESIGN

Literature review.

SETTING

Setting varied across studies by level of care and geographical locations.

INTERVENTIONS

No interventions were performed.

MAIN OUTCOME MEASURE(S)

Primary outcome measures were to summarize our current understanding of palatogenesis in humans and animal models, the pathophysiology of CP, and potential future treatment modalities.

RESULTS

Animal research has provided considerable insight into the pathophysiology, molecular and cellular mechanisms of CP that have allowed for the development of novel treatment strategies. However, much work has yet to be done to connect our mouse model investigations and discoveries to CP in humans. The success of innovative strategies for tissue regeneration in mice provides promise for an exciting new avenue for improved and more targeted management of cleft care with precision medicine in patients. However, significant barriers to clinical translation remain. Among the most notable challenges include the differences in some aspects of palatogenesis and tissue repair between mice and humans, suggesting that potential therapies that have worked in animal models may not provide similar benefits to humans.

CONCLUSIONS

Increased translation of pathophysiological and tissue regeneration studies to clinical trials will bridge a wide gap in knowledge between animal models and human disease. By enhancing interaction between basic scientists and clinicians, and employing our animal model findings of disease mechanisms in concert with what we glean in the clinic, we can generate a more targeted and improved treatment algorithm for patients with CP.

Kir2.1-NaV1.5 channelosome and its role in arrhythmias in inheritable cardiac diseases

Sudden cardiac death in children and young adults is a relatively rare but tragic event whose pathophysiology is unknown at the molecular level. Evidence indicates that the main cardiac sodium channel (NaV1.5) and the strong inward rectifier potassium channel (Kir2.1) physically interact and form macromolecular complexes (channelosomes) with common partners, including adapter, scaffolding, and regulatory proteins that help them traffic together to their eventual membrane microdomains. Most important, dysfunction of either or both ion channels has direct links to hereditary human diseases. For example, certain mutations in the KCNJ2 gene encoding the Kir2.1 protein result in Andersen-Tawil syndrome type 1 and alter both inward rectifier potassium and sodium inward currents. Similarly, trafficking-deficient mutations in the gene encoding the NaV1.5 protein (SCN5A) result in Brugada syndrome and may also disturb both inward rectifier potassium and sodium inward currents. Moreover, gain-of-function mutations in KCNJ2 result in short QT syndrome type 3, which is extremely rare but highly arrhythmogenic, and can modify Kir2.1-NaV1.5 interactions in a mutation-specific way, further highlighting the relevance of channelosomes in ion channel diseases. By expressing mutant proteins that interrupt or modify Kir2.1 or NaV1.5 function in animal models and patient-specific pluripotent stem cell-derived cardiomyocytes, investigators are defining for the first time the mechanistic framework of how mutation-induced dysregulation of the Kir2.1-NaV1.5 channelosome affects cardiac excitability, resulting in arrhythmias and sudden death in different cardiac diseases.

Valvulopathies and Genetics: Where are We?

Valvulopathies are among the most common cardiovascular diseases, significantly increasing morbidity and mortality. While many valvular heart diseases are acquired later in life, an important genetic component has been described, particularly in mitral valve prolapse and bicuspid aortic valve. These conditions can arise secondary to genetic syndromes such as Marfan disease (associated with mitral valve prolapse) or Turner syndrome (linked to the bicuspid aortic valve) or may manifest in a non-syndromic form. When cardiac valve disease is the primary cause, it can appear in a familial clustering or sporadically, with a clear genetic component. The identification of new genes, regulatory elements, post-transcriptional modifications, and molecular pathways is crucial to identify at-risk familial carriers and for developing novel therapeutic strategies. In the present review we will discuss the numerous genetic contributors of heart valve diseases.

The Genetics of Canine Pulmonary Valve Stenosis

There have been recent advancements in understanding the genetic contribution to pulmonary valve stenosis (PS) in brachycephalic breeds such as the French Bulldog and Bulldog. The associated genes are transcriptions factors involved in cardiac development, which is comparable to the genes that cause PS in humans. However, validation studies and functional follow up is necessary before this information can be used for screening purposes.

The interaction between the nervous system and the stomatognathic system: from development to diseases

The crosstalk between the nerve and stomatognathic systems plays a more important role in organismal health than previously appreciated with the presence of emerging concept of the "brain-oral axis". A deeper understanding of the intricate interaction between the nervous system and the stomatognathic system is warranted, considering their significant developmental homology and anatomical proximity, and the more complex innervation of the jawbone compared to other skeletons. In this review, we provide an in-depth look at studies concerning neurodevelopment, craniofacial development, and congenital anomalies that occur when the two systems develop abnormally. It summarizes the cross-regulation between nerves and jawbones and the effects of various states of the jawbone on intrabony nerve distribution. Diseases closely related to both the nervous system and the stomatognathic system are divided into craniofacial diseases caused by neurological illnesses, and neurological diseases caused by an aberrant stomatognathic system. The two-way relationships between common diseases, such as periodontitis and neurodegenerative disorders, and depression and oral diseases were also discussed. This review provides valuable insights into novel strategies for neuro-skeletal tissue engineering and early prevention and treatment of orofacial and neurological diseases.

Coarctation of the Aorta: Diagnosis and Management

Coarctation of the aorta (CoA) accounts for approximately 5-8% of all congenital heart defects. Depending on the severity of the CoA and the presence of associated cardiac lesions, the clinical presentation and age vary. Developments in diagnosis and management have improved outcomes in this patient population. Even after timely repair, it is important to regularly screen for hypertension. Patients with CoA require lifelong follow-up with a congenital heart disease specialist as these patients may develop recoarctation and complications at the repair site and remain at enhanced cardiovascular risk throughout their lifetime.

Molecular stratification of arrhythmogenic mechanisms in the Andersen Tawil syndrome

Andersen-Tawil syndrome (ATS) is a rare inheritable disease associated with loss-of-function mutations in KCNJ2, the gene coding the strong inward rectifier potassium channel Kir2.1, which forms an essential membrane protein controlling cardiac excitability. ATS is usually marked by a triad of periodic paralysis, life-threatening cardiac arrhythmias and dysmorphic features, but its expression is variable and not all patients with a phenotype linked to ATS have a known genetic alteration. The mechanisms underlying this arrhythmogenic syndrome are poorly understood. Knowing such mechanisms would be essential to distinguish ATS from other channelopathies with overlapping phenotypes and to develop individualized therapies. For example, the recently suggested role of Kir2.1 as a countercurrent to sarcoplasmic calcium reuptake might explain the arrhythmogenic mechanisms of ATS and its overlap with catecholaminergic polymorphic ventricular tachycardia. Here we summarize current knowledge on the mechanisms of arrhythmias leading to sudden cardiac death in ATS. We first provide an overview of the syndrome and its pathophysiology, from the patient's bedside to the protein and discuss the role of essential regulators and interactors that could play a role in cases of ATS. The review highlights novel ideas related to some post-translational channel interactions with partner proteins that might help define the molecular bases of the arrhythmia phenotype. We then propose a new all-embracing classification of the currently known ATS loss-of-function mutations according to their position in the Kir2.1 channel structure and their functional implications. We also discuss specific ATS pathogenic variants, their clinical manifestations, and treatment stratification. The goal is to provide a deeper mechanistic understanding of the syndrome toward the development of novel targets and personalized treatment strategies.

Ion Channels in the Development and Remodeling of the Aortic Valve

The role of ion channels is extensively described in the context of the electrical activity of excitable cells and in excitation-contraction coupling. They are, through this phenomenon, a key element for cardiac activity and its dysfunction. They also participate in cardiac morphological remodeling, in particular in situations of hypertrophy. Alongside this, a new field of exploration concerns the role of ion channels in valve development and remodeling. Cardiac valves are important components in the coordinated functioning of the heart by ensuring unidirectional circulation essential to the good efficiency of the cardiac pump. In this review, we will focus on the ion channels involved in both the development and/or the pathological remodeling of the aortic valve. Regarding valve development, mutations in genes encoding for several ion channels have been observed in patients suffering from malformation, including the bicuspid aortic valve. Ion channels were also reported to be involved in the morphological remodeling of the valve, characterized by the development of fibrosis and calcification of the leaflets leading to aortic stenosis. The final stage of aortic stenosis requires, until now, the replacement of the valve. Thus, understanding the role of ion channels in the progression of aortic stenosis is an essential step in designing new therapeutic approaches in order to avoid valve replacement.

The unique structural characteristics of the Kir 7.1 inward rectifier potassium channel: a novel player in energy homeostasis control

The inward rectifier potassium channel Kir7.1, encoded by the KCNJ13 gene, is a tetramer composed of two-transmembrane domain-spanning monomers, closer in homology to Kir channels associated with potassium transport such as Kir1.1, 1.2, and 1.3. Compared with other channels, Kir7.1 exhibits small unitary conductance and low dependence on external potassium. Kir7.1 channels also show a phosphatidylinositol 4,5-bisphosphate (PIP2) dependence for opening. Accordingly, retinopathy-associated Kir7.1 mutations mapped at the binding site for PIP2 resulted in channel gating defects leading to channelopathies such as snowflake vitreoretinal degeneration and Leber congenital amaurosis in blind patients. Lately, this channel's role in energy homeostasis was reported due to the direct interaction with the melanocortin type 4 receptor (MC4R) in the hypothalamus. As this channel seems to play a multipronged role in potassium homeostasis and neuronal excitability, we will discuss what is predicted from a structural viewpoint and its possible implications for hunger control.

Gene panel analysis of 119 index patients with suspected periodic paralysis in Japan

Introduction

Genetic factors are recognized as the major reason for patients with periodic paralysis. The goal of this study was to determine the genetic causes of periodic paralysis in Japan.

Methods

We obtained a Japanese nationwide case series of 119 index patients (108 men and 11 women) clinically suspected of periodic paralysis, and a gene panel analysis, targeting CACNA1S, SCN4A, and KCNJ2 genes, was conducted.

Results

From 34 cases, 25 pathogenic/likely pathogenic/unknown significance variants were detected in CACNA1S (nine cases), SCN4A (19 cases), or KCNJ2 (six cases), generating a molecular diagnostic rate of 28.6%. In total, seven variants have yet been found linked to periodic paralysis previously. The diagnostic yield of patients with hypokalemic and hyperkalemic periodic paralyzes was 26.2 (17/65) and 32.7% (17/52), respectively. A considerably higher yield was procured from patients with than without positive family history (18/25 vs. 16/94), onset age ≤20 years (24/57 vs. 9/59), or recurrent paralytic attacks (31/94 vs. 3/25).

Discussion

The low molecular diagnostic rate and specific genetic proportion of the present study highlight the etiological complexity of patients with periodic paralysis in Japan.

Identification of recurrent variants implicated in disease in bicuspid aortic valve patients through whole-exome sequencing

Bicuspid aortic valve (BAV) is the most common congenital heart defect in human beings, with an estimated prevalence in the general population of between 0.5 and 2%. Moreover, BAV is the most common cause of aortic stenosis in the pediatric population. Patients with BAV may have no symptoms for life, and some of them may progress to aortic stenosis. Genetic factors increase the susceptibility and development of BAV. However, the pathogenesis and BAV are still unclear, and more genetic variants are still needed for elucidating the molecular mechanism and stratification of patients. The present study carried out screening of variants implicated in disease in BAV patients. The whole-exome sequencing (WES) was performed in 20 BAV patients and identified 40 different heterozygous missense mutations in 36 genes (MIB2, FAAH, S100A1, RGS16, MAP3K19, NEB, TTN, TNS1, CAND2, CCK, KALRN, ATP10D, SLIT3, ROS1, FABP7, NUP205, IL11RA, NPR2, COL5A1, CUBN, JMJD1C, ANXA7, TRIM8, LGR4, TPCN2, APOA5, GPR84, LRP1, NCOR2, AKAP11, ESRRB, NGB, AKAP13, WWOX, KCNJ12, ARHGEF1). The mutations in these genes were identified as recurrent variants implicated in disease by in silico prediction tool analysis. Nine genes (MIB2, S100A1, TTN, CCK, NUP205, LGR4, NCOR2, ESRRB, and WWOX) among the 36 genes were identified as variants implicated in disease via unanimous agreement of in silico prediction tool analysis and sequenced in an independent cohort of 137 BAV patients to validate the results of WES. BAV patients carrying these variants demonstrated reduced left ventricular ejection fractions (LVEF) (63.8 ± 7.5% vs. 58.4 ± 5.2%, P < 0.001) and larger calcification volume [(1129.3 ± 154) mm³ vs. (1261.8 ± 123) mm³, P < 0.001]. The variants in TTN, NUP205 and NCOR2 genes are significantly associated with reduced LVEF, and the variants in S100A1, LGR4, ESRRB, and WWOX genes are significantly associated with larger calcification volume. We identified a panel of recurrent variants implicated in disease in genes related to the pathogenesis of BAV. Our data speculate that these variants are promising markers for risk stratification of BAV patients with increased susceptibility to aortic stenosis.

Inward rectifier potassium (Kir) channels in the retina: living our vision

Channel proteins are vital for conducting ions throughout the body and are especially relevant to retina physiology. Inward rectifier potassium (Kir) channels are a class of K+ channels responsible for maintaining membrane potential and extracellular K+ concentrations. Studies of the KCNJ gene (that encodes Kir protein) expression identified the presence of all of the subclasses (Kir 1-7) of Kir channels in the retina or retinal-pigmented epithelium (RPE). However, functional studies have established the involvement of the Kir4.1 homotetramer and Kir4.1/5.1 heterotetramer in Müller glial cells, Kir2.1 in bipolar cells, and Kir7.1 in the RPE cell physiology. Here, we propose the potential roles of Kir channels in the retina based on the physiological contributions to the brain, pancreatic, and cardiac tissue functions. There are several open questions regarding the expressed KCNJ genes in the retina and RPE. For example, why does not the Kir channel subtype gene expression correspond with protein expression? Catching up with multiomics or functional "omics" approaches might shed light on posttranscriptional changes that might influence Kir subunit mRNA translation within the retina that guides our vision.

Identification of the Differentially Expressed Genes in the leg muscles of Zhedong White Geese (Anser cygnoides) reared under different photoperiods

Light is a factor affecting muscle development and meat quality in poultry production. However, few studies have reported on the role of light in muscle development and meat quality in geese. In this experiment, 10 healthy 220-day-old Zhedong white geese were reared for 60 d under a long photoperiod (15L:9D, LL) and short photoperiod (9L:15D, SL). The gastrocnemius muscles were collected after slaughter to evaluate muscle fiber characteristics and meat color, and RNA-seq analysis. The results showed that compared to the LL group, the SL group had large muscle fiber diameter and cross-sectional area, few muscle fibers per unit area, high meat color a* value, and low L* value at 24 h postmortem. On comparing the 2 groups, 70 differentially expressed genes (DEGs) were identified. Compared to the SL group, the LL group had 25 upregulated and 45 downregulated genes. Gene Ontology (GO) enrichment analysis showed that these DEGs were mainly involved in cell, cell part, binding, cellular processes, and single-organism processes. Several significantly enriched athways were identified in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, such as the calcium and PI3k-Akt signaling pathways. The expression of five randomly selected DEGs was verified using quantitative real-time PCR, and the results were consistent with the RNA-seq data. This study provides a theoretical basis for studying the molecular mechanisms by which light affects muscle development and meat color in geese.

Characterization of Loss-Of-Function KCNJ2 Mutations in Atypical Andersen Tawil Syndrome

Andersen-Tawil Syndrome (ATS) is a rare disease defined by the association of cardiac arrhythmias, periodic paralysis and dysmorphic features, and is caused by KCNJ2 loss-of-function mutations. However, when extracardiac symptoms are atypical or absent, the patient can be diagnosed with Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT), a rare arrhythmia at high risk of sudden death, mostly due to RYR2 mutations. The identification of KCNJ2 variants in CPVT suspicion is very rare but important because beta blockers, the cornerstone of CPVT therapy, could be less efficient. We report here the cases of two patients addressed for CPVT-like phenotypes. Genetic investigations led to the identification of p. Arg82Trp and p. Pro186Gln de novo variants in the KCNJ2 gene. Functional studies showed that both variants forms of Kir2.1 monomers act as dominant negative and drastically reduced the activity of the tetrameric channel. We characterize here a new pathogenic variant (p.Pro186Gln) of KCNJ2 gene and highlight the interest of accurate cardiologic evaluation and of attention to extracardiac signs to distinguish CPVT from atypical ATS, and guide therapeutic decisions. We also confirm that the KCNJ2 gene must be investigated during CPVT molecular analysis.

Bicuspid Aortic Valve: Genetic and Clinical Insights

Bicuspid aortic valve (BAV) is the most common valvular congenital heart disease, with a prevalence of 0.5 to 2% in the general population. Patients with BAV are at risk for developing cardiovascular complications, some of which are life-threatening. BAV has a wide spectrum of clinical presentations, ranging from silent malformation to severe and even fatal cardiac events. Despite the significant burden on both the patients and the health systems, data are limited regarding pathophysiology, risk factors, and genetics. Family studies indicate that BAV is highly heritable, with autosomal dominant inheritance, incomplete penetrance, variable expressivity, and male predominance. Owing to its complex genetic model, including high genetic heterogenicity, only a few genes were identified in association with BAV, while the majority of BAV genetics remains obscure. Here, we review the different forms of BAV and the current data regarding its genetics. Given the clear heritably of BAV with the potential high impact on clinical outcome, the clinical value and cost effectiveness of cascade screening are discussed.

Cardiac potassium inward rectifier Kir2: Review of structure, regulation, pharmacology, and arrhythmogenesis

Potassium inward rectifier channel Kir2 is an important component of terminal cardiac repolarization and resting membrane stability. This functionality is part of balanced cardiac excitability and is a defining feature of excitable cardiac membranes. “Gain-of-function” or “loss-of-function” mutations in KCNJ2, the gene encoding Kir2.1, cause genetic sudden cardiac death syndromes, and loss of the Kir2 current I_K1 is a major contributing factor to arrhythmogenesis in failing human hearts. Here we provide a contemporary review of the functional structure, physiology, and pharmacology of Kir2 channels. Beyond the structure and functional relationships, we will focus on the elements of clinically used drugs that block the channel and the implications for treatment of atrial fibrillation with I_K1-blocking agents. We will also review the clinical disease entities associated with KCNJ2 mutations and the growing area of research into associated arrhythmia mechanisms. Lastly, the presence of Kir2 channels has become a tipping point for electrical maturity in induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) and highlights the significance of understanding why Kir2 in iPS-CMs is important to consider for Comprehensive In Vitro Proarrhythmia Assay and drug safety testing.

Mutation in KCNJ2 Gene in a Boy with Atypical Features of Andersen–Tawil Syndrome, ADHD, and ASD: An Expanding Phenotype

Andersen–Tawil syndrome, a potassium ion channelopathy, is caused by mutations in the KCNJ2 gene, and accounts for approximately 10% of channelopathies. Phenotype is variable. An 11-year-old boy presented with periodic paralysis without localizing neurological signs, associated in only two of three occasions with hypokalemia, on a background of a diagnosis of attention deficit hyperactivity disorder and autism spectrum disorder. There was a history of syncope and palpitations. This was a matter of diagnostic uncertainty due to the difficulty in interpreting his neurological signs, and inconsistency of abnormal potassium levels. In children/young people with recurrent episodes of weakness without localizing signs on physical examination, and syncope, the possibility of a channelopathy should be considered, even in the absence of serum electrolyte abnormalities. There is a possible link between KCNJ2 mutations and difficulties in attention and a specific neurocognitive profile.

Andersen-Tawil Syndrome With Novel Mutation in KCNJ2: Case Report

Andersen-Tawil syndrome (ATS) is a rare autosomal dominant disorder characterized by a classic symptom triad: periodic paralysis, ventricular arrhythmias associated with prolonged QT interval, and dysmorphic skeletal and facial features. Pathogenic variants of the inwardly rectifying potassium channel subfamily J member 2 (KCNJ2) gene have been linked to the ATS. Herein, we report a novel KCNJ2 causative variant in a proband and her father showing different ATS-associated symptoms. A 15-year-old girl was referred because of episodic weakness and periodic paralysis in both legs for 2-3 months. The symptoms occurred either when she was tired or after strenuous exercise. These attacks made walking or climbing stairs difficult and lasted from one to several days. She had a short stature (142 cm, <3rd percentile) and weighed 40 kg. The proband also showed orbital hypertelorism, dental crowding, mandibular hypoplasia, fifth-digit clinodactyly, and small hands. Scoliosis in the thoracolumbar region was detected by chest X-ray. Since she was 7 years old, she had been treated for arrhythmia-associated long QT interval and underwent periodic echocardiography. Brain MRI revealed cerebrovascular abnormalities indicating absence or hypoplasia of bilateral internal carotid arteries, and compensation of other collateral vessels was observed. There were no specific findings related to intellectual development. The proband's father also had a history of periodic paralysis similar to the proband. He did not show any cardiac symptoms. Interestingly, he was diagnosed with hyperthyroidism during an evaluation for paralytic symptoms. Clinical exome sequencing revealed a novel heterozygous missense variant: Chr17(GRCh37):g.68171593A>T, NM_000891.2:c.413A>T, p.(Glu138Val) in KCNJ2 in the proband and the proband's father.

Distinctive facial features in Andersen-Tawil syndrome: A three-dimensional stereophotogrammetric analysis

Andersen-Tawil syndrome (ATS) is a rare potassium channelopathy causing periodic paralysis, cardiac arrhythmias, and dysmorphic features. A detailed analysis of the face could facilitate diagnosis of ATS, as approximately 30% of patients do not show variants in KCNJ2 gene, and diagnosis is established by clinical findings. We aimed to characterize the face in ATS through a quantitative approach, as facial anomalies may be unnoticed on visual inspection. Facial images of 12 subjects with genetically confirmed ATS (six males, six females, age 5-67 years) were acquired through stereophotogrammetry. Using 38 soft-tissue landmarks, linear distances, angles, and ratios were calculated and expressed as z-score values, with reference to 477 healthy subjects matched for sex and age. All patients showed decreased lower facial height with shortening of philtrum (mean z-score ± SD: -1.5 ± 0.9), smaller mid and lower facial depths (-1.9 ± 0.7; -2.3 ± 0.9), short palpebral fissures (right -1.2 ± 0.4; left -1.6 ± 0.6), smaller mandibular ramus length (-2.1 ± 0.4), and increased nasal width/length ratio (1.4 ± 0.5) with smaller nostril axis length (right -1.8 ± 0.8, left -1.6 ± 0.7). Hypertelorism and low-set ears were detected in two-thirds of patients. The study quantified facial dysmorphysm in ATS, extending information about known features, and detecting unrecorded philtrum and nostril characteristics, which may be distinctive traits of the disorder.

Genetics and signaling mechanisms of orofacial clefts

Craniofacial development involves several complex tissue movements including several fusion processes to form the frontonasal and maxillary structures, including the upper lip and palate. Each of these movements are controlled by many different factors that are tightly regulated by several integral morphogenetic signaling pathways. Subject to both genetic and environmental influences, interruption at nearly any stage can disrupt lip, nasal, or palate fusion and result in a cleft. Here, we discuss many of the genetic risk factors that may contribute to the presentation of orofacial clefts in patients, and several of the key signaling pathways and underlying cellular mechanisms that control lip and palate formation, as identified primarily through investigating equivalent processes in animal models, are examined.

Every face tells a story-unravelling a case of bidirectional ventricular tachycardia

Bidirectional ventricular tachycardia is a rare form of tachycardia. We hereby report a case of bidirectional ventricular tachycardia in an 8-year-old boy wherein careful clinical exami-nation led to the diagnosis of Andersen Tawil syndrome. The case also demonstrates the efficacy of flecainide in managing bidirectional ventricular tachycardia in the setting of Andersen Tawil syndrome.

An unusual case of recurrent episodes of muscle weakness: Co-occurrence of Andersen-Tawil syndrome and glycogen storage disease type IXd

A 25-year-old male patient presented with periodic paralysis that increased in severity and frequency with age, accompanied with muscle pain and significantly elevated creatine kinase (CK) levels. Initial clinical and genetic examination confirmed Andersen-Tawil syndrome. Although his father carried the same genetic mutation (p.G300A), he experienced minor and infrequent attacks of paralysis. A change in the patient's symptoms, such as accompanying pain, contracture, and significant CK elevation, lead to a reconsideration of the diagnosis. A muscle biopsy of the biceps brachii in the patient revealed glycogen storage, but no tubular aggregates. Analysis of the phosphorylase kinase regulatory subunit alpha 1 (PHKA1) gene revealed a pathogenic mutation (p.C1082X), indicating glycogen storage disease type Ⅸd. The case demonstrates that co-occurrence of glycogen storage disease type Ⅸd may prolong attacks of muscle weakness, and cause serious muscle pain in patients with Andersen-Tawil syndrome.

Andersen-Tawil Syndrome Is Associated With Impaired PIP2 Regulation of the Potassium Channel Kir2.1

Andersen-Tawil syndrome (ATS) type-1 is associated with loss-of-function mutations in KCNJ2 gene. KCNJ2 encodes the tetrameric inward-rectifier potassium channel Kir2.1, important to the resting phase of the cardiac action potential. Kir-channels' activity requires interaction with the agonist phosphatidylinositol-4,5-bisphosphate (PIP₂). Two mutations were identified in ATS patients, V77E in the cytosolic N-terminal "slide helix" and M307V in the C-terminal cytoplasmic gate structure "G-loop." Current recordings in Kir2.1-expressing HEK cells showed that each of the two mutations caused Kir2.1 loss-of-function. Biotinylation and immunostaining showed that protein expression and trafficking of Kir2.1 to the plasma membrane were not affected by the mutations. To test the functional effect of the mutants in a heterozygote set, Kir2.1 dimers were prepared. Each dimer was composed of two Kir2.1 subunits joined with a flexible linker (i.e. WT-WT, WT dimer; WT-V77E and WT-M307V, mutant dimer). A tetrameric assembly of Kir2.1 is expected to include two dimers. The protein expression and the current density of WT dimer were equally reduced to ~25% of the WT monomer. Measurements from HEK cells and Xenopus oocytes showed that the expression of either WT-V77E or WT-M307V yielded currents of only about 20% compared to the WT dimer, supporting a dominant-negative effect of the mutants. Kir2.1 sensitivity to PIP₂ was examined by activating the PIP₂ specific voltage-sensitive phosphatase (VSP) that induced PIP₂ depletion during current recordings, in HEK cells and Xenopus oocytes. PIP₂ depletion induced a stronger and faster decay in Kir2.1 mutant dimers current compared to the WT dimer. BGP-15, a drug that has been demonstrated to have an anti-arrhythmic effect in mice, stabilized the Kir2.1 current amplitude following VSP-induced PIP₂ depletion in cells expressing WT or mutant dimers. This study underlines the implication of mutations in cytoplasmic regions of Kir2.1. A newly developed calibrated VSP activation protocol enabled a quantitative assessment of changes in PIP₂ regulation caused by the mutations. The results suggest an impaired function and a dominant-negative effect of the Kir2.1 variants that involve an impaired regulation by PIP₂. This study also demonstrates that BGP-15 may be beneficial in restoring impaired Kir2.1 function and possibly in treating ATS symptoms.

Clinical and neurophysiological variability in Andersen-Tawil syndrome

INTRODUCTION

Andersen-Tawil syndrome (ATS) is characterized by a triad of periodic paralysis, ventricular arrhythmias, and dysmorphism. However, patients often lack one or more of these features.

METHODS

Clinical and neurophysiological features were reviewed of five members in two families with heterozygous mutations in KCNJ2 (R218Q and R67W).

RESULTS

Only one patient had all features of the triad of ATS. One patient had low-set ears, and the others had minor anomalies. Bidirectional ventricular tachycardias were seen in two patients. Two patients (R67W) never had episodes of paralysis. The long exercise test was abnormal in three patients with episodes of paralysis, but normal in two without paralytic episodes.

DISCUSSION

ATS patients without skeletal muscle symptoms can have normal neurophysiological examinations. They can show variability in phenotype or the severity of arrhythmias. Such variability among patients who share the same gene mutations may result in underdiagnosis of ATS.

The bicuspid aortic valve: Is it an immunological disease process?

Bicuspid aortic valves (BAVs) are the most common congenital cardiac condition and are characterized by a structural abnormality whereby the aortic valve is composed of two leaflets instead of being trileaflet. It is linked to an increased risk for a variety of complications of the aorta, many with an immunological pathogenesis. The aim of this study is to review and analyze the literature regarding immunological processes involving BAVs, associated common pathologies, and their incidence in the population. This study will also examine current trends in surgical and therapeutic approaches to treatment and discuss the future direction of BAV treatment.

Purkinje physiology and pathophysiology

There has always been an appreciation of the role of Purkinje fibers in the fast conduction of the normal cardiac impulse. Here, we briefly update our knowledge of this important set of cardiac cells. We discuss the anatomy of a Purkinje fiber strand, the importance of longitudinal conduction within a strand, circus movement within a strand, conduction, and excitability properties of Purkinjes. At the cell level, we discuss the important components of the ion channel makeup in the nonremodeled Purkinjes of healthy hearts. Finally, we discuss the role of the Purkinjes in forming the heritable arrhythmogenic substrates such as long QT, heritable conduction slowing, CPVT, sQT, and Brugada syndromes.

Genetics of bicuspid aortic valve aortopathy

PURPOSE OF REVIEW

The incidence of aortic dilation and acute complications (rupture and dissection) is higher in patients with a bicuspid aortic valve (BAV), the most frequent congenital heart defect.The present review focuses on the current knowledge in the genetics of BAV, emphasizing the clinical implications for early detection and personalized care.

RECENT FINDINGS

BAV is a highly heritable trait, but the genetic causes remain largely elusive. NOTCH1 is the only proven candidate gene to be associated with both familial and sporadic BAV. Other genes have been reported to be associated with BAV, but some of these associations may result from coexisting disease.The application of modern high-throughput technologies (next generation sequencing, genome-wide copy number and genome-wide methylation arrays) have begun to dissect the genetic heterogeneity underlying BAV as well as the diverse molecular pathways involved in the progression of BAV aortopathy.

SUMMARY

The clinical variability seen in BAV aortopathy, in terms of phenotype and natural/clinical history, suggests complex interactions between primary genetic defects, other modifier genes, epigenetic factors (DNA methylation or histone modifications, microRNA) and environmental factors (disturbed flow). Integrated, more comprehensive studies are needed for elucidating these connections to develop more individualized and accurate risk assessment methods.

Whole-exome sequencing reveals microsatellite DNA markers for response to dofetilide initiation in patients with persistent atrial fibrillation: A pilot study

BACKGROUND

Dofetilide is a class III antiarrhythmic drug effective for the treatment of atrial fibrillation (AF). Dofetilide initiation (DI) associates with corrected QT interval (QTc) prolongation. Significant QTc prolongation during DI mandates dose adjustment or discontinuation of the drug. Microsatellite DNA are novel genetic markers associated with congenital and acquired health conditions.

HYPOTHESIS

DNA microsatellite polymorphism may associate with QTc response to dofetilide initiation in patients with persistent AF.

METHODS

We performed whole-exome sequencing in a cohort of patients with persistent AF undergoing DI. Electrocardiographic variables and clinical data were assessed. We defined patients as eligible for DI when no significant QTc prolongation (>20% compared with baseline) was seen with a 500-μg dose. We defined patients as ineligible for DI when significant QTc prolongation was seen during DI with 500 μg. We investigated polymorphisms for 11 919 DNA microsatellite loci in relation to QTc response to DI.

RESULTS

During the study, 14 consecutive patients with persistent AF presenting for DI were enrolled. Whole-exome sequencing revealed 14 different microsatellite loci in the 2 groups. All genes or proximal genes that harbor these loci are known to have expression in the human heart. Two genes, MYH6 and TRAK2, are known to have expression in the atria. TRAK2 is known to interact with KCNJ2, the inward-rectifier potassium channel 1.

CONCLUSIONS

Microsatellite DNA polymorphisms seem to associate with QTc response to DI therapy in patients with persistent AF who are deemed otherwise eligible for dofetilide therapy.

Periodic paralysis

The periodic paralyses are a group of skeletal muscle channelopathies characterizeed by intermittent attacks of muscle weakness often associated with altered serum potassium levels. The underlying genetic defects include mutations in genes encoding the skeletal muscle calcium channel Ca_v1.1, sodium channel Na_v1.4, and potassium channels K_ir2.1, K_ir3.4, and possibly K_ir2.6. Our increasing knowledge of how mutant channels affect muscle excitability has resulted in better understanding of many clinical phenomena which have been known for decades and sheds light on some of the factors that trigger attacks. Insights into the pathophysiology are also leading to new therapeutic approaches.

Cardiac, mandibular and thymic phenotypical association indicates that cranial neural crest underlies bicuspid aortic valve formation in hamsters

Bicuspid aortic valve (BAV) is the most prevalent human congenital cardiac malformation. It may appear isolated, associated with other cardiovascular malformations, or forming part of syndromes. Cranial neural crest (NC) defects are supposed to be the cause of the spectrum of disorders associated with syndromic BAV. Experimental studies with an inbred hamster model of isolated BAV showed that alterations in the migration or differentiation of the cardiac NC cells in the embryonic cardiac outflow tract are most probably responsible for the development of this congenital valvular defect. We hypothesize that isolated BAV is not the result of local, but of early alterations in the behavior of the NC cells, thus also affecting other cranial NC-derived structures. Therefore, we tested whether morphological variation of the aortic valve is linked to phenotypic variation of the mandible and the thymus in the hamster model of isolated BAV, compared to a control strain. Our results show significant differences in the size and shape of the mandible as well as in the cellular composition of the thymus between the two strains, and in mandible shape regarding the morphology of the aortic valve. Given that both the mandible and the thymus are cranial NC derivatives, and that the cardiac NC belongs to the cephalic domain, we propose that the causal defect leading to isolated BAV during embryonic development is not restricted to local alterations of the cardiac NC cells in the cardiac outflow tract, but it is of pleiotropic or polytopic nature. Our results suggest that isolated BAV may be the forme fruste of a polytopic syndrome involving the cranial NC in the hamster model and in a proportion of affected patients.

Bicuspid aortic valve syndrome: a multidisciplinary approach for a complex entity

Bicuspid aortic valve (BAV) or bicuspid aortopathy is the most common congenital heart disease. It can be clinically silent and it is often identified as an incidental finding in otherwise healthy, asymptomatic patients. However, it can be dysfunctioning at birth, even requiring neonatal intervention, or, in time, lead to aortic stenosis, aortic insufficiency, and endocarditis, and also be associated with aortic aneurysm and aortic dissection. Given its prevalence and significant complications, it is estimated that BAV is responsible for more deaths and morbidity than the combined effects of all the other congenital heart defects. Pathology of BAV is still not well known and many questions are unresolved. In this manuscript we review some aspects on bicuspid aortopathy, a heterogeneous and frequent disease in which like some authors have previously described, complex gene environment are present. Further investigations and, what is more, multidisciplinary teams are needed to improve our knowledge on this really fascinating disease.

Andersen-Tawil syndrome: Clinical presentation and predictors of symptomatic arrhythmias - Possible role of polymorphisms K897T in KCNH2 and H558R in SCN5A gene

BACKGROUND

Andersen-Tawil syndrome (ATS) is rare channelopathy caused by KCNJ2 mutation and probably KCNJ5. It is characterized by arrhythmias, neurological symptoms, and dysmorphic features. The present study retrospectively examined the characteristics of 11 unrelated families with ATS.

METHODS

This study consisted of 11 probands positive for KCNJ2 variants and 33 family members (mean age 30.0±17.3 years, female n=31). Additional genetic screening of 3 LQTS genes (KCNQ1, KCNH2, SCN5A) was performed in 9 families. Predictors of arrhythmias [premature ventricular beats>2000/24h, biventricular and polymorphic ventricular tachycardia (VT)], syncope, and/or cardiac arrest (CA) were evaluated.

RESULTS

In KCNJ2 mutation carriers vs non-carriers (n=25 vs n=19) significant differences were observed in U-wave manifestations in V2-V4, T_peak-T_end duration, QTUc duration (p<0.0001), dysmorphic features, and neurological symptoms. Compared to asymptomatic carriers (n=9), in those with arrhythmias and/or syncope and/or CA (n=16) micrognathia (p=0.004), periodic paralysis (p=0.019), palpitation (p=0.005), U-wave n V2-V4 (p=0.049) were more frequent; QTU (p=0.045) and T_peak-T_end (p=0.014) were also longer (n=9). In the subgroup of carriers with syncope and/or cardiac arrest (n=10, 90% women), K897T-KCNH2 polymorphism (p=0.02), periodic paralysis (p=0.004), muscle weakness (p=0.04), palpitations (p=0.04), arrhythmias (biventricular VT, p=0.003; polymorphic VT, p=0.009) were observed more frequently. T_peak-T_end duration was longer (p=0.007) and the percentage of patients with premature ventricular contraction >2000/24h was higher (p=0.005).

CONCLUSION

A higher risk of arrhythmia, syncope, and/or CA is associated with the presence of micrognathia, periodic paralysis, and prolonged T_peak-T_end time. Our findings suggest that K897T may contribute to the occurrence of syncope.

TRPM4 non-selective cation channel variants in long QT syndrome

Background

Long QT syndrome (LQTS) is an inherited arrhythmic disorder characterized by prolongation of the QT interval, a risk of syncope, and sudden death. There are already a number of causal genes in LQTS, but not all LQTS patients have an identified mutation, which suggests LQTS unknown genes.

Methods

A cohort of 178 LQTS patients, with no mutations in the 3 major LQTS genes (KCNQ1, KCNH2, and SCN5A), was screened for mutations in the transient potential melastatin 4 gene (TRPM4).

Results

Four TRPM4 variants (2.2% of the cohort) were found to change highly conserved amino-acids and were either very rare or absent from control populations. Therefore, these four TRPM4 variants were predicted to be disease causing. Furthermore, no mutations were found in the DNA of these TRPM4 variant carriers in any of the 13 major long QT syndrome genes. Two of these variants were further studied by electrophysiology (p.Val441Met and p.Arg499Pro). Both variants showed a classical TRPM4 outward rectifying current, but the current was reduced by 61 and 90% respectively, compared to wild type TRPM4 current.

Conclusions

This study supports the view that TRPM4 could account for a small percentage of LQTS patients. TRPM4 contribution to the QT interval might be multifactorial by modulating whole cell current but also, as shown in Trpm4^−/− mice, by modulating cardiomyocyte proliferation. TRPM4 enlarges the subgroup of LQT genes (KCNJ2 in Andersen syndrome and CACNA1C in Timothy syndrome) known to increase the QT interval through a more complex pleiotropic effect than merely action potential alteration.

Pathology and molecular mechanisms of coarctation of the aorta and its association with the ductus arteriosus

Coarctation of the aorta (CoA) is defined as a congenital stenosis of the thoracic aorta and is one of the most common congenital cardiovascular diseases. Despite successful surgical treatment for CoA, arterial abnormalities, including refractory hypertension, aortic aneurysm, and proatherogenic phenotypic changes, frequently affect patients' quality of life. Emerging evidence from morphological and molecular biological investigations suggest that the area of CoA is characterized by phenotypic modulation of smooth muscle cells, intimal thickening, and impaired elastic fiber formation. These changes extend to the pre-and post-stenotic aorta and impair arterial elasticity. The aim of this review is to present current findings on the pathology and molecular mechanisms of vascular remodeling due to CoA. In particular, we will discuss the association between CoA and the ductus arteriosus since the most common site for the stenosis is in the proximity of the ductus arteriosus.

Gene-Targeted Analysis of Clinically Diagnosed Long QT Russian Families

Long QT syndrome (LQTS) has great genetic heterogeneity: more than 500 mutations have been described in several genes. Despite many advances, a genetic diagnosis still cannot be established in 25-30% of patients. The aim of the present study was to perform genetic evaluation in 9 Russian families with LQTS; here we report the results of 4 positive probands and their relatives (a total of 16 individuals). All subjects underwent clinical examination, 12-lead ECG, and Holter monitoring. Genetic analysis of the 14 genes mainly involved in LQTS was performed using a next-generation sequencing approach. We identified two new mutations (KCNQ1 gene) and 6 known mutations (AKAP9, ANK2, KCNE1 and KCNJ2 genes) in 4 out of 9 probands, some of which have already been described in association with LQTS. Segregation studies suggest a possible causative role for KCNQ1 p.(Leu342Pro), AKAP9 p.(Arg1609Lys), KCNE1 p.(Asp85Asn), and KCNJ2 p.(Arg82Gln) variations. Our study confirmed the high genetic heterogeneity of this disease and highlights the difficulties to reveal clear pathogenic genotypes also in large pedigrees. To the best of our knowledge, this is the first genetic study of LQTS patients from Russian families.

Clinical features and long exercise test in Chinese patients with Andersen-Tawil syndrome

INTRODUCTION

Andersen-Tawil syndrome (ATS) is a rare multisystem channelopathy characterized by periodic paralysis, ventricular arrhythmias, and developmental dysmorphology. There are few reports concerning ATS in the Chinese population. We analyzed clinical features and evaluated the long exercise test as a tool for diagnosis of periodic paralysis in ATS.

METHODS

Direct sequencing of KCNJ2 was performed in 12 subjects from mainland China with suspected ATS. Clinical features, therapeutic responses, and long exercise tests (LET) were retrospectively analyzed.

RESULTS

Twelve patients were genetically confirmed to have ATS. A small mandible and clinodactyly were demonstrated in all patients. Premature ventricular contractions were the most prevalent form of cardiac arrhythmia. The LET revealed an early amplitude decrement.

CONCLUSIONS

Chinese ATS patients shared some common clinical features with reported subjects in other countries. An early amplitude decrement in LET may be useful for diagnosis of ATS. Muscle Nerve 54: 1059-1063, 2016.

Genetic testing in congenital heart disease: A clinical approach

Congenital heart disease (CHD) is the most common type of birth defect. Traditionally, a polygenic model defined by the interaction of multiple genes and environmental factors was hypothesized to account for different forms of CHD. It is now understood that the contribution of genetics to CHD extends beyond a single unified paradigm. For example, monogenic models and chromosomal abnormalities have been associated with various syndromic and non-syndromic forms of CHD. In such instances, genetic investigation and testing may potentially play an important role in clinical care. A family tree with a detailed phenotypic description serves as the initial screening tool to identify potentially inherited defects and to guide further genetic investigation. The selection of a genetic test is contingent upon the particular diagnostic hypothesis generated by clinical examination. Genetic investigation in CHD may carry the potential to improve prognosis by yielding valuable information with regards to personalized medical care, confidence in the clinical diagnosis, and/or targeted patient follow-up. Moreover, genetic assessment may serve as a tool to predict recurrence risk, define the pattern of inheritance within a family, and evaluate the need for further family screening. In some circumstances, prenatal or preimplantation genetic screening could identify fetuses or embryos at high risk for CHD. Although genetics may appear to constitute a highly specialized sector of cardiology, basic knowledge regarding inheritance patterns, recurrence risks, and available screening and diagnostic tools, including their strengths and limitations, could assist the treating physician in providing sound counsel.