Academic literature on the topic 'KCNH2 gene'

We report a 37-year-old woman with an out-of-hospital cardiac arrest caused by ventricular fibrillation due to digenic inheritance of long QT syndrome type 2 (KCNH2 gene) and type 6 (KCNE2 gene). During hospitalization, prolonged QTc intervals and frequent episodes of ventricular tachyarrhythmias manifested. Genetic testing identified a mutation of the KCNH2 gene and an unclassified variant, most likely pathogenic, of the KCNE2 gene. This digenic inheritance is extremely rare.

Abstract Background: The voltage-gated, rapid-delayed rectifier current (IKr) is important for repolarization of the heart, and mutations in the genes coding for the K+-ion channel conducting this current, i.e., KCNH2 for the α-subunit HERG and KCNE2 for the β-subunit MiRP1, cause acquired and congenital long Q-T syndrome (LQTS) and other cardiac arrhythmias. Methods: We developed a robust single-strand conformation polymorphism-heteroduplex screening analysis, with identical thermocycling conditions for all PCR reactions, covering all of the coding exons in KCNH2 and KCNE2. The method was used to screen 40 unrelated LQTS patients. Results: Eleven mutations, of which six were novel, were found in KCNH2. Interestingly, six mutations were found in the region of the gene coding for the Per-Arnt-Sim (PAS) and PAS-S1 regions of the HERG protein, stressing the need to examine the entire gene when screening for mutations. No mutations were found in KCNE2, suggesting that direct involvement of MiRP1 in LQTS is rare. Furthermore, four novel single-nucleotide polymorphisms (SNPs) and one amino acid polymorphism (R1047L) were identified in KCNH2, and one novel SNP and one previously known amino acid polymorphism (T8A) were found in KCNE2. Conclusions: The potential role of rare polymorphisms in the HERG/MiRP1 K+-channel should be clarified with respect to drug interactions and susceptibility to arrhythmia and sudden death.

Цель исследования: поиск причинных мутаций в генах-кандидатах внезапной сердечной смерти (ВСС) у мужчин, умерших в возрасте до 45 лет. Группа ВСС (30 образцов) была сформирована c использованием критериев ВСС ВОЗ и Европейского общества кардиологов. Средний возраст 31,3±5,3 года. Геномную ДНК выделяли из ткани миокарда методом фенол-хлороформной экстракции. Выполнили секвенирование клинического экзома. На первом этапе проанализировали результаты секевнирования 16 генов, мутации в которых приводят к ССЗ, ассоциированным с повышенным риском ВСС: KCNQ1, KCNH2, SCN5A, AKAP9, ANK2, CACNA1C, CALM1, CALM2, CAV3, KCNE1, KCNE2, KCNJ2, KCNJ5, SCN4B, SNTA1, SCN10A. Из 30 образцов с ВСС при анализе результатов секвенирования 16 генов было обнаружено 6 вероятно патогенных миссенс-мутаций в 7 образцах (23,3 %). В гене SCN10A обнаружено 2 мутации, в KCNH2, KCNE1, AKAP9, SNTA1 - по одной мутации. Подводя первые итоги пилотного исследования ВСС можно сделать следующие предварительные выводы: необходимо продолжение исследований в области молекулярной аутопсии в России, для повышения результативности поиска причинных мутаций, желательны снижение возраста случаев ВСС включаемых в исследование, а также работа с семьями умерших ВСС. Objective: Search for causal mutations in candidate genes for sudden cardiac death (SCD) in men who die before the age of 45. Materials and methods. The SCD group (30 samples) was formed using the criteria for sudden cardiac death of the WHO and the European Society of Cardiology. The average age is 31,3±5,3 years. Genomic DNA was isolated from myocardial tissue using phenol-chloroform extraction. Clinical exome sequencing was performed. At the first stage, the results of sequencing of 16 genes were analyzed, mutations in which result in CVD associated with an increased risk of SCD: KCNQ1, KCNH2, SCN5A, AKAP9, ANK2, CACNA1C, CALM1, CALM2, CAV3, KCNE1, KCNE2, KCNJ5, KCNJ5, SNTA1, SCN10A. Results. Of 30 samples with SCD, when analyzing the results of sequencing 16 genes, 6 probably pathogenic missense mutations were found in 7 samples (23.3%). 2 mutations were found in the SCN10A gene, one mutation in KCNH2, KCNE1, AKAP9, SNTA1. Findings. Summing up the first results of a pilot SCD study, the following preliminary conclusions can be drawn: it is necessary to continue research in the field of molecular autopsy in Russia, in order to increase the effectiveness of the search for causative mutations, it is desirable to reduce the age of SCD cases included in the study, as well as work with families of deceased SCD.

Highlights. Probably causal mutations of QT interval prolongation in genes associated with LQTS were found in men of the Siberian population.Aim. To detect and study mutations in individuals with borderline prolongation of the QT interval in Siberian males.Methods. The study was conducted on the material of the international project HAPIEE in the period from 2003 to 2005 and screening of young people aged 25–44, performed in Novosibirsk. The total sample of men was 1353 people aged 25 to 69 years. From each age subgroup (25–29, 30–34, ..., 65–69 years old) 2–3 samples with the highest QT values were selected . The study group consisted of 30 men who subsequently underwent sequencing of a panel of genes. The search for mutations was carried out in genes associated with long QT syndrome (LQTS): KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, KCNJ2, CACNA1, SCN4B, KCNJ5, ANK2, CAV3, SNTA1, AKAP9, CALM1 and CALM2. All identified single nucleotide variants were verified by direct Sanger sequencing.Results. Three rare variants in the LQTS genes have been identified: p.P197L of the KCNQ1 gene, p.R176W, and p.D1003GfsX116 of the KCNH2 gene.Conclusion. In Caucasian men from the Novosibirsk population with borderline prolongation of the QT interval, probably causal substitutions in the LQTS genes – KCNH2 and KCNQ1, contributing to the prolongation of the QT interval, were found. To clarify the spectrum and frequency of occurrence of various mutations in genes, life-threatening arrhythmias in the population, additional studies are needed on extended samples.

The Elk subfamily of the Eag K+ channel gene family is represented in mammals by three genes that are highly conserved between humans and rodents. Here we report the distribution and functional properties of a member of the human Elk K+ channel gene family, KCNH8. Quantitative RT-PCR analysis of mRNA expression patterns showed that KCNH8, along with the other Elk family genes, KCNH3 and KCNH4, are primarily expressed in the human nervous system. KCNH8 was expressed at high levels, and the distribution showed substantial overlap with KCNH3. In Xenopus oocytes, KCNH8 gives rise to slowly activating, voltage-dependent K+ currents that open at hyperpolarized potentials (half-maximal activation at -62 mV). Coexpression of KCNH8 with dominant-negative KCNH8, KCNH3, and KCNH4 subunits led to suppression of the KCNH8 currents, suggesting that Elk channels can form heteromultimers. Similar experiments imply that KCNH8 subunits are not able to form heteromultimers with Eag, Erg, or Kv family K+ channels.

Long QT syndrome (LQTS) exhibits great phenotype variability among family members carrying the same mutation, which can be partially attributed to genetic factors. We functionally analyzed the KCNH2 (encoding for Kv11.1 or hERG channels) and TBX20 (encoding for the transcription factor Tbx20) variants found by next-generation sequencing in two siblings with LQTS in a Spanish family of African ancestry. Affected relatives harbor a heterozygous mutation in KCNH2 that encodes for p.T152HfsX180 Kv11.1 (hERG). This peptide, by itself, failed to generate any current when transfected into Chinese hamster ovary (CHO) cells but, surprisingly, exerted “chaperone-like” effects over native hERG channels in both CHO cells and mouse atrial-derived HL-1 cells. Therefore, heterozygous transfection of native (WT) and p.T152HfsX180 hERG channels generated a current that was indistinguishable from that generated by WT channels alone. Some affected relatives also harbor the p.R311C mutation in Tbx20. In human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), Tbx20 enhanced human KCNH2 gene expression and hERG currents (IhERG) and shortened action-potential duration (APD). However, Tbx20 did not modify the expression or activity of any other channel involved in ventricular repolarization. Conversely, p.R311C Tbx20 did not increase KCNH2 expression in hiPSC-CMs, which led to decreased IhERG and increased APD. Our results suggest that Tbx20 controls the expression of hERG channels responsible for the rapid component of the delayed rectifier current. On the contrary, p.R311C Tbx20 specifically disables the Tbx20 protranscriptional activity over KCNH2. Therefore, TBX20 can be considered a KCNH2-modifying gene.

Previous studies suggest that ether-a-go-go related gene (ERG) KCNH2 potassium channels contribute to the control of motility patterns in the gastrointestinal tract of animal models. The present study examines whether these results can be translated into a role in human gastrointestinal muscles. Messages for two different variants of the KCNH2 gene were detected: KCNH2 V1 human ERG (HERG) (28) and KCNH2 V2 (HERGUSO) (13). The amount of V2 message was greater than V1 in both human jejunum and brain. The base-pair sequence that gives rise to domains S3– S5 of the channel was identical to that previously published for human KCNH2 V1 and V2. KCNH2 protein was detected immunohistochemically in circular and longitudinal smooth muscle and enteric neurons but not in interstitial cells of Cajal. In the presence of TTX (10−6 M), atropine (10−6M). and l-nitroarginine (10−4 M) human jejunal circular muscle strips contracted phasically (9 cycles/min) and generated slow waves with superimposed spikes. Low concentrations of the KCNH2 blockers E-4031 (10−8 M) and MK-499 (3 × 10−8 M) increased phasic contractile amplitude and the number of spikes per slow wave. The highest concentration of E-4031 (10−6 M) produced a 10–20 mV depolarization, eliminated slow waves, and replaced phasic contractions with a small tonic contracture. E-4031 (10−6 M) did not affect [14C]ACh release from enteric neurons. We conclude that KCNH2 channels play a fundamental role in the control of motility patterns in human jejunum through their ability to modulate the electrical behavior of smooth muscle cells.

Проведен поиск мутаций в генах KCNQ1, KCNH2 и SCN5A методом массового параллельного секвенирования (МПС) у 10 пациентов из 8 семей с диагнозом «синдром удлиненного интервала QT» (СУИQT). Для пробоподготовки использована методика целевого обогащения участков ДНК, относящихся к исследуемым генам. В результате проведенной работы выявлено 8 мутаций: 5 из них расположены в гене KCNQ1, 2 мутации - в гене KCNH2, 1 мутация - в гене SCN5A. Во всех случаях были найдены уникальные мутации, не повторяющиеся у неродственных пациентов. Результаты проведенной работы указывают на эффективность использования таргетных панелей для поиска генетических аномалий при СУИQT. We searched for mutations in the KCNQ1, KCNH2 and SCN5A genes using mass parallel sequencing (MPS) in 10 patients from 8 families with a diagnosis of “long QT syndrome” (LQTS). For sample preparation, we used the targeted enrichment of DNA regions method related to the studied genes. As a result of the work, 8 mutations were revealed: 5 of them are located in the KCNQ1 gene, 2 mutations in the KCNH2 gene, 1 mutation in the SCN5A gene. In all cases, we found unique mutations that did not recur in unrelated patients. The results of this work indicate the effectiveness of using targeted panels to search for genetic abnormalities in LQTS.

Background: The KCNH2 -encoded Kv11.1 hERG (human ether-a-go-go related gene) potassium channel is a critical regulator of cardiomyocyte action potential duration (APD). The majority of type 2 long-QT syndrome (LQT2) stems from trafficking defective KCNH2 mutations. Recently, Food and Drug Administration-approved cystic fibrosis protein trafficking chaperone, lumacaftor, has been proposed as novel therapy for LQT2. Here, we test the efficacy of lumacaftor treatment in patient-specific induced pluripotent stem cell-cardiomyocytes (iPSC-CMs) derived from 2 patients with known LQT2 trafficking defective mutations and a patient with novel KCNH2 variant, p.R685P. Methods: Patient-specific iPSC-CM models of KCNH2-G604S, KCNH2-N633S, and KCNH2-R685P were generated from 3 unrelated patients diagnosed with severe LQT2 (rate-corrected QT>500 ms). Lumacaftor efficacy was also tested by ANEPPS, FluoVolt, and ArcLight voltage dye-based APD90 measurements. Results: All 3 mutations were hERG trafficking defective in iPSC-CMs. While lumacaftor treatment failed to rescue the hERG trafficking defect in TSA201 cells, lumacaftor rescued channel trafficking for all mutations in the iPSC-CM model. All 3 mutations conferred a prolonged APD90 compared with control. While lumacaftor treatment rescued the phenotype of KCNH2-N633S and KCNH2-R685P, lumacaftor paradoxically prolonged the APD90 in KCNH2-G604S iPSC-CMs. Lumacaftor-mediated APD90 rescue was affected by rapidly activating delayed rectifier K+ current blocker consistent with the increase of rapidly activating delayed rectifier K+ current by lumacaftor is the underlying mechanism of the LQT2 rescue. Conclusions: While lumacaftor is an effective hERG channel trafficking chaperone and may be therapeutic for LQT2, we urge caution. Without understanding the functionality of the mutant channel to be rescued, lumacaftor therapy could be harmful.

Andersen-Tawil syndrome (ATS) is a rare channelopathy, sometimes referred to as long QT syndrome type 7. ATS is an autosomal dominant disease predominantly caused by mutations in the KCNJ2 gene. Patients with ATS present with episodes of muscle weakness, arrythmias, including prolonged QT intervals, and various skeletal abnormalities. Unlike other channelopathies, ATS has a relatively mild clinical course and low risk of sudden cardiac death. In this study, we describe a female patient with typical symptoms of ATS with the addition of unusually severe arrhythmias. Extensive DNA testing was performed to find the possible cause of this unique presentation. In addition to a known mutation in KCNJ2, the patient carried a variant in KCNH2. The combination of genetic variants may lead to the severe clinical manifestation of ATS. Additional genetic information allowed accurate genetic counselling to be provided to the patient.

El cromosoma humà 21 (HSA21), és el cromosoma autosòmic humà més petit. La trisomia total o parcial del HSA21 està associada a síndrome de Down (SD). El fet de tenir la seqüència del HSA21 pràcticament complerta, ha accelerat molt el procés d'identificació de gens, pas previ per a l 'establiment de relacions causa-efecte entre els gens del HSA21 i els fenotips clínics de la SD.

L'objectiu final d'aquesta tesi és la identificació i caracterització de nous gens del HSA21.

Els resultats obtinguts es poden resumir en :

· S'ha participat en la construcció d'un contig de cosmidis de tres regions del HSA21, cobrint al voltant de 3 Mb.

· S' ha participat en la construcció d'un mapa transcripcional de les tres regions. Es va realitzar una selecció de cDNAs, aïllant en total 45 cDNAs parcials no redundants, dels quals 25 no mostraven similitud amb cap seqüència de les bases de dades. Tots s'expressaven en una barreja de RNA poliA+ de cervell, pulmó, fetge i ronyó fetals. Els intents d'aïllar els cDNAs complerts corresponents a cada un dels clons varen resultar negatius.

· S' ha aïllat un nou gen del HSA21, KCNE2, identificat inicialmente mitjançant una anàlisi computacional de la seqüència genòmica AP000052. El cDNA complert té 850 pb. KCNE2 codifica per a una proteïna de 123 aa amb elevada homologia a KCNE1, una subunitat ß de canals de potassi depenents de voltage. L'estructura genòmica té un únic exó codificant i mapa a 21q22.1. KCNE2 s'expressa com un RNA de 1.2 kb, majoritàriament a estómac. La seqüència de la proteína KCNE2 conté 2 llocs consens de N-glicosilació, es prediu una regió transmembrana i un lloc consens de fosforilació per PKC. En experiments de western amb extractes de cèl·lules de mamífer transfectades, la proteïna es detecta com a tres bandes entre 16 kDa i 20 kDa, essent la més petita la del pes molecular esperat. Experiments amb tunicamicina han demostrat que KCNE2 es glicosila en asparagines, in vivo. Es van generar dos mutants en els llocs consens de glicosilació, N6Q i N29Q, que han demostrat que ambdós llocs són susceptibles de ser glicosilats. Experiments d'immunofluorescència indirecta suggereixen que KCNE2 s'inserta en la membrana amb el seu extrem N-terminal cap al medi extracel·lular i que amb un únic residu glicosilat n'hi ha prou per integrar-s'hi. Experiments de RT-PCR semiquantitativa indiquen que no hi ha sobre-expressió en SD ni de KCNE1 ni de KCNE2, a cors fetals SD. Es van buscar mutacions a KCNE2 en pacients de sordesa no sindròmica i es va trobar un canvi de nucleòtid A22G, que dóna lloc a un canvi d'aminoàcid T8A. Aquest canvi afectaria el punt de glicosilació.

· Es va identificar un nou gen, por homologia a KCNE1 i KCNE2, al qual se li va donar el nom de KCNE3. El cDNA complert té 1646 pb i conté una pauta de lectura oberta de 103 aa. L'estructura genòmica és similar a la de KCNE1 i KCNE2, amb un únic exó codificant, per tant podria tractar-se d'una família de gens paràlegs. KCNE3 es va mapar a la regió 11q13-14, utilitzant el pannell d'híbrids de radiació G3 d'Stanford. KCNE3 s'expresa com a un mRNA de 3 Kb a colon, intestí prim, ovari i a sang perifèrica. La seqüència de aminoácidos conté 3 llocs consens de N-glicosilació, es prediu una regió transmembrana i un lloc consens de fosforilació per PKC. S' ha demostrat que KCNE3 es N-glicosila en cèl·lules de mamífer i que s'inserta a la membrana amb l'extrem N-terminal dirigit cap al medi extracel·lular. S'ha trobat un polimorfisme T198C, que provoca el canvi d'aminoàcid F66L, amb una freqüència del 15% en la población general.

L’Encefalopatia Epilettica (EE) è una condizione clinica severa che causa un grave ritardo cognitivo e neurologico. Recentemente, sono state identificate mutazioni associate ad EE nei geni kcnq2 e kcnq3 che codificano rispettivamente per le subunità del potassio voltaggio-dipendenti Kv7.2 e Kv7.3. Ciascuna subunità è formata da 6 segmenti transmembrana e da un lungo dominio C-terminale a cui possono legarsi diverse molecole regolatorie quali il fostatidil-inositolo-(4,5)-bisfosfato (PIP2), un importante attivatore dei canali Kv7, e la calmodulina (CaM). I canali maturi sono formati dall’assemblaggio eteromerico delle subunità Kv7.2 e Kv7.3 e sottendono una corrente del potassio detta “corrente M” che inibisce l’eccitabilità neuronale. Lo scopo del presente lavoro è stato quello di investigare le conseguenze funzionali e la sensibilità farmacologica delle seguenti mutazioni: • Kv7.2 R325G identificata in tre soggetti con EE; • due varianti in eterozigosi composta nel gene kcnq3 riscontrate in un soggetto con EE (Kv7.3 V359L/Kv7.3 D542N) e la mutazione Kv7.2 D535N, corrispondente alla variante Kv7.3 D542N, descritta in tre casi con epilessia neonatale; • Kv7.2 G310S riscontrata in un paziente con EE. Al fine di studiare tali mutazioni cellule CHO sono state trasfettate con le subunità di interesse e le correnti espresse dalle cellule sono state registrate mediante la tecnica del patch-clamp in configurazione whole-cell. Dagli esperimenti di elettrofisiologia è emerso che i canali omomerici mutanti non sono funzionali rispetto ai controlli rappresentati dai canali Kv7.2 o Kv7.3 wild-type (wt). Al fine di riprodurre il bilancio genico dei probandi in studio, le subunità mutanti sono state espresse in configurazione eteromerica con le subunità Kv7.2 e Kv7.3 wt ed è stata osservata una significativa riduzione della densità di corrente dei canali eteromerici mutanti rispetto al canale eteromerico wt. Sulla base di questi risultati, è stato testato il farmaco attivatore retigabina che ha consentito di ripristinare, ai livelli del wt, la corrente elicitata dai canali eteromerici mutanti. Per comprendere il possibile meccanismo responsabile dell’effetto indotto dalle mutazioni è stato utilizzato un modello strutturale delle subunità Kv7.2 o Kv7.3 da cui è emerso che i residui di interesse sono localizzati in un sito di legame per il PIP2 e adiacenti al sito di legame per la CaM. Pertanto, sono stati condotti ulteriori esperimenti di elettrofisiologia utilizzando la chinasi PIP5K che incrementa i livelli di PIP2 o la fosfatasi DrVSP che ne riduce i livelli. La co-espressione della PIP5K con i canali Kv7.2 omomerici mutanti ha consentito un significativo aumento della densità di corrente. Al contrario, tale effetto non è stato osservato per i canali Kv7.3 mutanti. Gli esperimenti con la DrVSP hanno mostrato un maggiore effetto di inibizione ed una più lenta cinetica di recupero della corrente espressa dai canali eteromerici mutanti rispetto a quella misurata per il canale wt. Tali risultati suggeriscono che le mutazioni in studio alterano la regolazione della corrente M mediata dal PIP2. Un significativo recupero della funzionalità del canale è stato anche osservato dalla co-espressione dei canali Kv7.2 D535N e Kv7.2 G310S con la CaM1234 (una calmodulina mutata che non lega il calcio), suggerendo che per tali canali mutanti risulta compromessa anche la regolazione dipendente dalla calmodulina. In conclusione, le mutazioni studiate causano una completa perdita di funzione dei canali probabilmente in seguito all’alterata regolazione operata dal PIP2 e, in alcuni casi, dalla calmodulina. Infine, tali risultati forniscono un razionale per l’uso di attivatori, quali la retigabina o suoi analoghi, per il trattamento di pazienti affetti da EE e portatori di tali mutazioni.
Epileptic Encephalopathy (EE) is a severe form of epilepsy in which epileptiform activity contributes to a progressive cerebral dysfunction. Recently, mutations in the kcnq2 or kcnq3 genes have been identified in patients affected by EE. These genes encode for neuronal Kv7.2 or Kv7.3 subunits characterized by the presence of six transmembrane segments and a long C-terminus domain to which several modulatory proteins are associated, such as the phosphatidylinositol-4-5-bis-phosphate (PIP2), that is a know Kv7 activator, and the calmodulin (CaM). The heteromeric channels underlie the neuronal M current, a potassium current which inhibits neuronal excitability. The aim of this work is to study the functional consequences and the pharmacological sensitivity of Kv7.2 or Kv7.3 channels incorporating the following mutations: • Kv7.2 R325G identified in three patients affected by EE; • two mutations in the kcnq3 gene in compound heterozygosis identified in a patient affected by EE (Kv7.3 V359L/Kv7.3 D542N) and the Kv7.2 D535N corresponding to the Kv7.3 D542N variant and described in three cases with EE; • Kv7.2 G310S identified in a patient with EE. To study this mutation channel subunits were expressed in CHO cells by transient transfection. One day after transfection, we recorded the currents by whole cell patch-clamp. Patch-clamp recordings revealed that homomeric mutant channel are not functional when compared to homomeric Kv7.2 or Kv7.3 wild-type (wt) channels. To reproduce the genetic balance of EE-affected patients, mutant subunits were co-expressed with Kv7.2 or Kv7.3 wt subunits. The results obtained suggest that heteromeric mutant channels carried currents size smaller than those from heteromeric wt channels. Based on these results, we therefore tested the activator drug, called retigabine, that was able to restore, at wt levels, the currents carried by heteromeric mutant channels. To better understand the pathogenic mechanism induced by the mutations, we used a structural model in which was possible to reproduce a portion of Kv7.2 or Kv7.3 channels. The residues of our interest are involved in the binding-site of PIP2 and are near to the binding-site of CaM. To this aim, we used two experimental tools: a PIP2-synthesizing enzyme, called PIP5K, that increses PIP2 levels, or a phosphatase, like DrVSP, which reduces PIP2 levels. PIP5K co-expression with Kv7.2 homomeric mutant channels significantly increased current size. On the other end, this effect was not observed for Kv7.3 mutant channels. DrVSP experiments showed that heteromeric mutant currents is more easily inhibeted by DrVSP e more slowly recovered, when compared to heteromeric wt channels. These results suggest that the studied mutations interfere with the PIP2-dependent regulation. Furthermore, a significant current size increase was observed by the co-expression of CaM1234 (a mutated calmodulin that does not bind calcium) with Kv7.2 D535N and Kv7.2 G310S mutant channels, suggesting that these channels also interfere with CaM regulation. In conclusions, the mutations herein investigated causes a loss of function by interfering with the PIP2 regulation and, in some cases, also with the CaM regulation. Moreover, these results provide a rationale for the use of Kv7 channels activators, like retigabine or retigabine derivates, for the pharmacological treatment of patients affected by EE carrying Kv7 loss-of-function mutations.

The present thesis describes the identification and characterization of sequence variants in the cardiac ion channel genes KCNH2 and SCN5A. The variants were found in sudden cardiac death victims, in patients with ion channel diseases and in their family members. The results support the growing awareness that carriership of a single mutation often fails to predict the clinical phenotype and that additional genetic modifications may influence the clinical manifestation of the disease.

Short QT syndrome (SQTS) is an extremely rare inherited arrhythmogenic entity. Nowadays, less than 200 families affected worldwide have been reported. This syndrome is characterized by the presence of a short QT interval leading to malignant ventricular tachyarrhythmias, syncope and sudden cardiac death. It is one of the most lethal heart diseases in children and young adults. Both incomplete penetrance and variable expressivity are hallmarks of this entity, making it difficult to diagnose and manage. Currently, rare variants in nine genes have been associated with SQTS (CACNA1C, CACNA2D1, CACNB2, KCNH2, KCNJ2, KCNQ1, SLC22A5, SLC4A3 and SCN5A). However, only pathogenic variants in four genes (KCNH2, KCNQ1, KCNJ2 and SLC4A3) have been found to definitively cause SQTS. The remaining genes lack a clear association with the disease, making clinical interpretation of the variants challenging. The diagnostic yield of genetic tests is currently less than 30%, leaving most families clinically diagnosed with SQTS without a conclusive genetic diagnosis. We reviewed and updated the main genetic features of SQTS, as well as recent evidence on increasingly targeted treatment.

Long QT syndrome (LQTS) is a collective term used for a group of inherited arrhythmogenic disorders characterized by a prolonged cardiac action potential duration that predisposes affected individuals to the development of life-threatening arrhythmias, especially during phases of adrenergic activation (exercise, emotions). From the genetic standpoint, LQTS is mainly transmitted as an autosomal dominant trait, caused by point mutations in genes coding for protein channels that regulate the duration of cardiac action potentials. To date, 17 genes have been associated with LQTS, but the first three genotypes discovered (LQT1, LQT2, and LQT3) account for the majority of genotype-positive cases. LQT1 and LQT2 (75% of LQTS cases) are caused by loss-of-function mutations in genes (KCNQ1 and KCNH2) coding for potassium channels (I_Ks and I_Kr) involved in the repolarization phase of cardiomyocytes, while LQT3 is caused by gain-of-function mutations affecting the gene SCN5A coding for the Na_v1.5 sodium channel, which is the major determinant of depolarization of cardiomyocytes. Genetic testing has a great potential for the management of patients with LQTS and may contribute to better define the diagnosis, the risk stratification, and the choice of therapy.