Jervell And Lange-Nielsen Syndrome Research Articles

Dominant-negative suppression by KCNQ1-ΔF339 potassium channels linked to Romano–Ward syndrome

Hereditary long QT syndrome (LQTS) is a genetically heterogeneous disease characterized by prolonged QT intervals and an increased risk for ventricular arrhythmias and sudden cardiac death. Mutations in the voltage-gated potassium channel subunit KCNQ1 induce the most common form of LQTS. KCNQ1 is associated with two different entities of LQTS, the autosomal-dominant Romano-Ward syndrome (RWS), and the autosomal-recessive Jervell and Lange-Nielsen syndrome (JLNS) characterized by bilateral deafness in addition to cardiac arrhythmias. In this study, we investigate and discuss dominant-negative I(Ks) current reduction by a KCNQ1 deletion mutation identified in a RWS family. Single-strand conformation polymorphism analysis and direct sequencing were used to screen LQTS genes for mutations. Mutant KCNQ1 channels were heterologously expressed in Xenopus oocytes, and potassium currents were recorded using the two-microelectrode voltage clamp technique. A heterozygous deletion of three nucleotides (CTT) identified in the KCNQ1 gene caused the loss of a single phenylalanine residue at position 339 (KCNQ1-deltaF339). Electrophysiological measurements in the presence and absence of the regulatory beta-subunit KCNE1 revealed that mutant and wild type forms of an N-terminal truncated KCNQ1 subunit (isoform 2) caused much stronger dominant-negative current reduction than the mutant form of the full-length KCNQ1 subunit (isoform 1). This study highlights the functional relevance of the truncated KCNQ1 splice variant (isoform 2) in establishment and mode of inheritance in long QT syndrome. In the RWS family presented here, the autosomal-dominant trait is caused by multiple dominant-negative effects provoked by heteromultimeric channels formed by wild type and mutant KCNQ1-isoforms in combination with KCNE1.

Assessment of ventricular repolarization in a large group of children with early onset deafness.

This study examined the ECG traces of 397 deaf children (age 12.5 +/- 2.9 years, range 6-19 years), after exclusion of cases with Jervell and Lange-Nielsen syndrome (JLNS), and compared them to those of 361 normal hearing counterparts (age 12.5 +/- 2.7 years; range 7-18 years). An observer, who was unaware of the hearing status of the subjects, measured QT and QTc intervals and calculated dispersions of QT and QTc from standard 12-lead ECGs recorded at a speed of 25 mm/s at rest. Although the mean QT was found to be longer in deaf children than that observed in the control group (P < 0.0001), the mean QTc was significantly shorter (P < 0.0001). The mean heart rate was significantly lower in deaf children. When QT and QTc data were recompared after the children were grouped according to the heart rate, the observed difference became less significant or disappeared. In conclusion, there are no major abnormalities for repolarization parameters in children with congenital sensorineural deafness, when compared to hearing counterparts, if heart rates are similar. Based on these results, routine ECG screening of deaf children for repolarization abnormalities may be unnecessary unless they have a history of syncope or positive family history of syncope and/or early sudden death.

Compound heterozygous mutations in KvLQT1 cause Jervell and Lange-Nielsen syndrome

Jervell and Lange-Nielsen syndrome (JLNS) is characterized by sensorineural deafness, QT prolongation, abnormal T waves, ventricular tachyarrhythmias, and autosomal recessive inheritance. Previously homozygous mutations in the potassium channel-encoding genes, KvLQT1 (α-subunit) and KCNE1 (β-subunit), have been described in consanguineous families with JLNS. We screened two nonconsanguineous families with JLNS for mutations in KvLQT1, using single-strand conformation polymorphism analysis, denaturing high-performance liquid chromatography, and DNA sequencing. In one family, a missense mutation was identified in exon 6 of KvLQT1 on the maternal side, resulting in a glycine to aspartic acid substitution at codon 269 (G269D). The apparently normal father had an incompletely penetrant missense mutation in exon 3 of KvLQT1, introducing a premature stop codon at position 171. In the other family, a missense mutation resulting in the substitution of asparagine for aspartic acid at codon 202 (D202N) was identified in the mother and maternal grandmother, who had QTc prolongation (borderline in the mother), while the father and paternal grandfather, who were clinically normal, had a deletion of nucleotide 585, resulting in a frameshift and premature termination. In both families, the proband inherited both mutations. In this report we provide evidence that not only homozygous but also compound heterozygous mutations in KvLQT1 may cause JLNS in nonconsanguineous families. Incomplete penetrance in individuals with mutations appears to be frequent, indicating a higher prevalence of mutations than estimated previously. Interestingly, mutations resulting in truncation of the protein appear to be benign, with heterozygous carriers being asymptomatic.

A spectrum of functional effects for disease causing mutations in the Jervell and Lange-Nielsen syndrome.

Jervell and Lange-Nielsen syndrome (JLNS) is a recessively inherited long QT syndrome (LQTS) characterised by profound sensorineural deafness and predisposition to syncope and sudden cardiac death. Mutation analysis has established the presence of mutations in affected individuals in the genes KCNQ1 and KCNE1: the potassium channel complex responsible for the cardiac I(Ks) current involved in repolarisation of the ventricular action potential. Our objective was to determine the functional effects of disease causing mutations in JLNS. In this study we have investigated the electrophysiological effects of eight distinct JLNS mutations after expression of cRNA in Xenopus laevis oocytes. KCNE1 mutant T59P/L60P showed no dominant negative effect and was a pure loss of function mutation. KCNQ1 mutant E261D showed a strong dominant-negative effect. KCNQ1 mutant R243H produced a moderate dominant-negative effect, right shifted the steady-state activation curve and led to an increased deactivation rate. The behaviour of KCNQ1 mutants 572-576del, 1008delC, R518X, Q530X, R594Q depended on the relative quantities of mutant and wild-type proteins (with a weak dominant-negative effect present at 1:3 but not 1:1 injection ratios). These data indicate the presence of an additional assembly domain before S2-S3 and the importance of the S4-S5 region in channel function and gating. Our data suggest a spectrum of behaviour for disease causing mutations from simple loss of function through to prominent dominant negative behaviour.

Targeted disruption of the Kcnq1 gene produces a mouse model of Jervell and Lange-Nielsen Syndrome.

KCNQ1 encodes KCNQ1, which belongs to a family of voltage-dependent K(+) ion channel proteins. KCNQ1 associates with a regulatory subunit, KCNE1, to produce the cardiac repolarizing current, I(Ks). Loss-of-function mutations in the human KCNQ1 gene have been linked to Jervell and Lange-Nielsen Syndrome (JLNS), a disorder characterized by profound bilateral deafness and a cardiac phenotype. To generate a mouse model for JLNS, we created a line of transgenic mice that have a targeted disruption in the Kcnq1 gene. Behavioral analysis revealed that the Kcnq1(-/-) mice are deaf and exhibit a shaker/waltzer phenotype. Histological analysis of the inner ear structures of Kcnq1(-/-) mice revealed gross morphological anomalies because of the drastic reduction in the volume of endolymph. ECGs recorded from Kcnq1(-/-) mice demonstrated abnormal T- and P-wave morphologies and prolongation of the QT and JT intervals when measured in vivo, but not in isolated hearts. These changes are indicative of cardiac repolarization defects that appear to be induced by extracardiac signals. Together, these data suggest that Kcnq1(-/-) mice are a potentially valuable animal model of JLNS.

KCNQ1/KCNE1 potassium channels in mammalian vestibular dark cells

The high [K +] in the inner ear endolymph is essential for mechanosensory transduction in hearing and balance. Several ion channels, including a slowly activating, voltage-dependent, outwardly conducting K + channel composed of the KCNQ1 (KvLQT1) and KCNE1 (IsK/minK) subunits, are expressed at the apical surface of vestibular dark cells. We investigated the underlying molecular mechanisms of this conductance using in situ hybridization, RT-PCR, and immunocytochemistry and by tracking the ultrastructural changes of vestibular structures in kcne1(−/−) mice. In the wild type mice, the KCNE1 and KCNQ1 proteins are expressed specifically at the apical membrane of dark cells, as early as gestational day (GD) 17 for KCNE1 while KCNQ1 mRNAs can be detected at GD 18. This is the first demonstration that the two protein components of this potassium channel co-localize in a polarized fashion at the cellular level. Although the vestibular end-organs are normal at birth in kcne1(−/−) mice, they begin to show modifications during postnatal development: we observed an increase in the height of the dark cells, in their number of mitochondria, and in basolateral membrane infoldings. Subsequently, the epithelium degenerates and the endolymphatic space collapses. Similar changes are known to occur in the cardio-auditory Jervell–Lange-Nielsen syndrome which is caused by mutations in the same channel.

A founder mutation of the potassium channel KCNQ1 in long QT syndrome: Implications for estimation of disease prevalence and molecular diagnostics

OBJECTIVESWe took advantage of the genetic isolate of Finns to characterize a common long QT syndrome (LQTS) mutation, and to estimate the prevalence of LQTS.BACKGROUNDThe LQTS is caused by mutations in different ion channel genes, which vary in their molecular nature from family to family.METHODSThe potassium channel gene KCNQ1 was sequenced in two unrelated Finnish patients with Jervell and Lange-Nielsen syndrome (JLNS), followed by genotyping of 114 LQTS probands and their available family members. The functional properties of the mutation were studied using a whole-cell patch-clamp technique.RESULTSWe identified a novel missense mutation (G589D or KCNQ1-Fin) in the C-terminus of the KCNQ1 subunit. The voltage threshold of activation for the KCNQ1-Fin channel was markedly increased compared to the wild-type channel. This mutation was present in homozygous form in two siblings with JLNS, and in heterozygous form in 34 of 114 probands with Romano-Ward syndrome (RWS) and 282 family members. The mean (± SD) rate-corrected QT intervals of the heterozygous subjects (n = 316) and noncarriers (n = 423) were 460 ± 40 ms and 410 ± 20 ms (p < 0.001), respectively.CONCLUSIONSA single missense mutation of the KCNQ1 gene accounts for 30% of Finnish cases with LQTS, and it may be associated with both the RWS and JLNS phenotypes of the syndrome. The relative enrichment of this mutation most likely represents a founder gene effect. These circumstances provide an excellent opportunity to examine how genetic and nongenetic factors modify the LQTS phenotype.

Mutational spectrum in the cardioauditory syndrome of Jervell and Lange-Nielsen.

Jervell and Lange-Nielsen syndrome (JLNS) is an autosomal recessive syndrome characterised by profound congenital sensorineural deafness and prolongation of the QT interval on the electrocardiogram, representing abnormal ventricular repolarisation. In a study of ten British and Norwegian families with JLNS, we have identified all of the mutations in the KCNQ1 gene, including two that are novel. Of the nine mutations identified in this group of 10 families, five are nonsense or frameshift mutations. Truncation of the protein proximal to the recently identified C-terminal assembly domain is expected to preclude assembly of KCNQ1 monomers into tetramers and explains the recessive inheritance of JLNS. However, study of a frameshift mutation, with a dominant effect phenotypically, suggests the presence of another assembly domain nearer to the N-terminus.

A recessive C-terminal Jervell and Lange-Nielsen mutation of the KCNQ1 channel impairs subunit assembly.

The LQT1 locus (KCNQ1) has been correlated with the most common form of inherited long QT (LQT) syndrome. LQT patients suffer from syncopal episodes and high risk of sudden death. The KCNQ1 gene encodes KvLQT1 alpha-subunits, which together with auxiliary IsK (KCNE1, minK) subunits form IK(s) K(+) channels. Mutant KvLQT1 subunits may be associated either with an autosomal dominant form of inherited LQT, Romano-Ward syndrome, or an autosomal recessive form, Jervell and Lange-Nielsen syndrome (JLNS). We have identified a small domain between residues 589 and 620 in the KvLQT1 C-terminus, which may function as an assembly domain for KvLQT1 subunits. KvLQT1 C-termini do not assemble and KvLQT1 subunits do not express functional K(+) channels without this domain. We showed that a JLN deletion-insertion mutation at KvLQT1 residue 544 eliminates important parts of the C-terminal assembly domain. Therefore, JLN mutants may be defective in KvLQT1 subunit assembly. The results provide a molecular basis for the clinical observation that heterozygous JLN carriers show slight cardiac dysfunctions and that the severe JLNS phenotype is characterized by the absence of KvLQT1 channel.

Jervell and Lange-Nielsen syndrome: neurologic and cardiologic evaluation

Recurrent syncope, malignant ventricular arrhythmias, and sudden death are complications of the long QT syndrome (LQTS). Two well-known syndromes with long QT intervals are known. The Jervell and Lange-Nielsen syndrome (JLNS) is characterized by prolongation of the QT interval, deafness, and autosomal-recessive inheritance, and the Romano-Ward syndrome is characterized by a prolonged QT interval, autosomal-dominant inheritance, and no deafness. In the present study assessment was performed of the diagnostic importance of the ventricular derepolarization parameters, clinical features, and prevalence of JLNS among 132 children with congenital hearing loss (CHL). In the CHL group the mean QT, QTc, JT, and JTc intervals and the dispersion values (QT-d, JT-d, QTc-d, and JTc-d) were significantly longer than those of control subjects (n = 96) ( P < 0.05). Patients with CHL and JLNS (n = 5) had significantly longer mean values of QT, QTc, JT, and JTc intervals and dispersion values than those of CHL without JLNS (n = 127) and control subjects ( P < 0.05). The results suggest that assessment of ventricular derepolarization parameters in children with CHL will be helpful in the early detection of JLNS because infants with CHL cannot accurately describe the symptoms of syncope.

Congenital long-QT syndrome: a case report illustrating diagnostic pitfalls

This article reviews the clinical course of a 10-year-old child with a lifelong history of seizures and congenital deafness who presented after an episode of sudden cardiac arrest secondary to long-QT syndrome-induced torsade de pointes. Jervell–Lange–Nielsen syndrome is a rare cardioauditory syndrome in which affected subjects are susceptible to recurrent syncope and sudden death from ventricular dysrhythmias, usually before the second decade of life. Careful evaluation of suspected subjects is important because of the variability of the QTc interval. Recent research has identified specific gene sequences that encode ion channels responsible for both prolonged QTc interval and deafness. Treatment of symptomatic cardiac disease with β-blockers in combination with pacemakers and automated internal cardioverter defibrillators can markedly improve quality of life and suppress ventricular dysrhythmias even in the most severely affected subjects. The recent identification of gene sequences identifying some congenital long-QT syndromes may improve screening methods for affected patients and lead to potential therapeutic intervention.

Dominant-negative isoforms modulate phenotype in inherited cardiac arrhythmias

Romano-Ward syndrome (RWS) is a dominantly inherited cause of cardiac arrhythmias that can lead to syncope and sudden death. It results from mutations in the KCNQ1 gene; mutations in this gene also cause Jervell and Lange-Nielsen syndrome (JLN), an autosomal recessive condition that is characterized by cardiac arrhythmias and congenital deafness. KCNQ1 encodes the pore-forming K+ ion channel subunit, KvLQT1. Together with its β-subunit, IsK, KvLQT1 produces the slow component of the delayed rectifier K+ current in the heart. RWS and JLN mutations reduce this current, prolonging repolarization and predisposing to abnormalities in cardiac rhythm.When expressed in vitro, RWS and JLN mutations are indistinguishable, leading to the absence or significant reduction of the K+ current. So how can the very different phenotypic consequences in heterozygous carriers be explained? An N-terminal, truncated splice variant of KvLQT1, isoform 2, that is constitutively expressed in the heart is known to exert a dominant-negative effect on full-length KvLQT1 protein (isoform 1). All RWS and JLN mutations are common to both isoforms. In this paper1xMutations in a dominant-negative isoform correlate with phenotype in inherited cardiac arrhythmias. Mohammad-Panah, R. et al. Am. J. Hum. Genet. 1999; 64: 1015–1023Abstract | Full Text | Full Text PDF | PubMed | Scopus (59)See all References1, the effects of six mutations on isoform 2 are examined by functional expression in COS-7 cells and by measuring the K+ current generated. With the three RWS mutations, isoform 2 retained significant dominant-negative activity whereas this was abolished by the three JLN mutations. The authors propose a mechanism whereby in JLN heterozygotes, both isoforms produced from the mutant allele are inactive. However, as the wild-type KvLQT1 isoforms function normally there is little or no deleterious effect from the reduction in dosage. In RWS heterozygotes, isoform 1 is inactivated but mutant isoform 2 retains its dominant-negative effect and can exert this upon wild-type isoform 1. The resulting imbalance downregulates KvLQT1 function significantly below the level seen in JLN heterozygotes, thus producing a dominant phenotype. This complex interplay between isoforms has not previously been implicated in modulating genetic disease, but several other genes have dominant-negative isoforms and the possibility that a similar mechanism could be operating in other conditions is intriguing.

The therapeutic potential for targetting potassium channels: Are dendrotoxins a suitable basis for drug design?

Voltage-dependent potassium ion channels have been implicated in several diseases of genetic or autoimmune origin. There are genetic defects of specific potassium channel genes in episodic ataxia with myokymia, long QT syndrome, Jervell–Lange–Nielsen syndrome, and familial hyperinsulinemic hypoglycemia of infancy. Antibodies against voltage-gated potassium channels have been detected in Isaacs syndrome (acquired neuromyotonia). Voltage-gated potassium channels have also been regarded as therapeutic targets for immunosuppressants (targetting Kv1.3 channels) and in some neurodegenerative diseases (targetting Kv1.1 or 1.2 channels). Specific blockers of potassium channels may be designed from an understanding of the molecular recognition properties of highly specific potassium channel blocking toxins such as dendrotoxin. The dendrotoxin family of toxins and their genetic relatives in the Kunitz family of proteinase inhibitors have been studied extensively in recent years. Structural studies and functional studies with mutated toxins provide information that should help the rational design of analogues with the desired properties.

Imprinting of mouse Kvlqt1 is developmentally regulated.

Mouse distal chromosome 7 contains a cluster of at least five imprinted genes. The syntenic region in humans, at 11p15.5, has been implicated in several genetic disorders. Consistent with the imprinted status of the genes in the region, Beckwith-Wiedemann syndrome (BWS) and Wilms tumor are each associated with loss of maternal information. Also mapping to 11p15.5 are long QT and Jervell and Lange-Nielsen (JLN) syndromes. In contrast to BWS and Wilms tumor, these syndromes do not show any parent of origin bias. Recently positional cloning has identified KVLQT1 as the 11p15.5 gene responsible for increased susceptibility to long QT and JLN syndromes. Other studies associate KVLQT1 with BWS. Human KVLQT1 is paternally imprinted in embryos. In this study we present a contig and transcript map of distal mouse 7 and we physically and genetically map mouse Kvlqt1 to the region. Mouse Kvlqt1 is strongly expressed in heart, lung, gut, kidney and uterus. While its early developmental expression is maternal in origin, the paternal allele becomes increasingly active during development. Late juvenile and adult animals show complete biallelism, suggesting an explanation for the lack of parent of origin bias in JLN and long QT.

Heterozygous mutation in the pore of potassium channel gene KvLQT1 causes an apparently normal phenotype in long QT syndrome.

Mutations in KvLQT1, a gene encoding a potassium channel, cause both the recessive Jervell and Lange-Nielsen (JLN) syndrome and the dominant Romano-Ward (RW) syndrome. These diseases are characterised by a prolonged QT interval on the ECG, syncopes and sudden death due to cardiac arrhythmias. The JLN syndrome is also associated with a congenital bilateral deafness. We report here a novel missense mutation, W305S, in the pore region of KvLQT1 identified by PCR-SSCP analysis in two consanguineous JLN families. In contrast to several missense mutations found in the same region of KvLQT1 in RW patients which are associated with severe cardiac phenotypes, the W305S mutation is responsible for an apparently normal phenotype in heterozygous JLN carriers.

New Insights on Pattern of Inheritance in Long-QT Syndrome.

The congenital long-QT syndrome is characterized by prolonged ventricular repolarization and life-threatening arrhythmias. Two variants of the disease are recognized: the autosomal recessive Jervell and Lange-Nielsen syndrome, characterized by prolonged repolarization and congenital deafness; and the autosomal dominant Romano-Ward syndrome, also marked by prolonged repolarization but with normal hearing. Recent studies have shown …

IsK and KvLQT1: mutation in either of the two subunits of the slow component of the delayed rectifier potassium channel can cause Jervell and Lange-Nielsen syndrome.

The Jervell and Lange-Nielsen syndrome (JLNS) comprises profound congenital sensorineural deafness associated with syncopal episodes. These are caused by ventricular arrhythmias secondary to abnormal repolarisation, manifested by a prolonged QT interval on the electrocardiogram. Recently, in families with JLNS, Neyroud et al. reported homozygosity for a single mutation in KVLQT1 , a gene which has previously been shown to be mutated in families with dominantly inherited isolated long QT syndrome [Neyroud et al . (1997) Nature Genet ., 15, 186-189]. We have analysed a group of families with JLNS and shown that the majority are consistent with mutation at this locus: five families of differing ethnic backgrounds were homozygous by descent for markers close to the KVLQT1 gene and a further three families from the same geographical region were shown to be homozygous for a common haplotype and to have the same homozygous mutation of the KVLQT1 gene. However, analysis of a single small consanguineous family excluded linkage to the KVLQT1 gene, establishing genetic heterogeneity in JLNS. The affected children in this family were homozygous by descent for markers on chromosome 21, in a region containing the gene IsK . This codes for a transmembrane protein known to associate with KVLQT1 to form the slow component of the delayed rectifier potassium channel. Sequencing of the affected boys showed a homozygous mutation, demonstrating that mutation in the IsK gene may be a rare cause of JLNS and that an indistinguishable phenotype can arise from mutations in either of the two interacting molecules.

Autosomal recessive long-QT syndrome (Jervell Lange-Nielsen syndrome) is genetically heterogeneous.

Jervell Lange-Nielsen syndrome (JLNS) is a recessive disorder with congenital deafness and long-QT syndrome (LQTS 1). Mutations in the potassium-channel gene KVLQT1 (LQTS 1) have been identified in JLNS and in autosomal-dominant LQTS as well. We performed haplotype analysis with microsatellite markers in a Lebanese family with JLNS, but failed to detect linkage at LQTS 1. Moreover, using this approach, we excluded two other ion-channel genes involved in autosomal-dominant LQTS, HERG (LQTS 2) and SCN5A (LQTS 3). Our findings indicate that JLNS is genetically heterogeneous and that, in this family, an unknown LQTS gene causes the disease.

A novel mutation in the potassium channel gene KVLQT1 causes the Jervell and Lange-Nielsen cardioauditory syndrome.

The Jervell and Lange-Nielsen (JLN) syndrome (MIM 220400) is an inherited autosomal recessive disease characterized by a congenital bilateral deafness associated with a QT prolongation on the electrocardiogram, syncopal attacks due to ventricular arrhythmias and a high risk of sudden death. JLN syndrome is a rare disease, which seems to affect less than one percent of all deaf children. Linkage to chromosome 11p15.5 markers was found by analysing four consanguinous families. Recombinants allowed us to map the JLN gene between D11S922 and D11S4146, to a 6-cM interval where KVLQT1, a potassium channel gene causing Romano-Ward (RW) syndrome, the dominant form of long QT syndrome, has been previously localized. An homozygous deletion-insertion event (1244, -7 +8) in the C-terminal domain of this gene was detected in three affected children of two families. We found that KVLQT1 is expressed in the stria vascularis of mouse inner ear by in situ hybridization. Taken together, our data indicate that KVLQT1 is responsible for both JLN and RW syndromes and has a key role not only in the ventricular repolarization but also in normal hearing, probably via the control of endolymph homeostasis.

The Jervell and Lange-Nielsen syndrome

The association of prolongation of the QT interval with recurrent attacks of syncope, sudden death, and malignant ventricular arrhythmias is known as the long QT syndrome. The syndrome may be familial with or without congenital deafness, or idiopatic. The syndrome with deafness (Jervell and Lange-Nielsen syndrome) is inherited through an autosomal recessive mechanism. In this study, we attempted to identify patients with the Jervell Lange-Nielsen syndrome amongst 154 deaf mute school children. Two patients had a corrected QT interval of 0.52 and congenital sensorineural hearing loss with the other electrocardiographic changes characteristic of the syndrome, such as inverted or bifid T wave. There was no evidence of electrocardiographic (ECG) abnormality in family members, except only one case of parental deafness. This is the first and preliminary report that analyzed the incidence of the Jervell and Lange-Nielsen syndrome amongst 154 deaf mute school children in Turkey. Our study was conducted to identify patients with this syndrome amongst children of another deaf mute school in Turkey.