Bmc Medical Genetics Identification of a Novel Kcnq1 Mutation Associated with Both Jervell and Lange-nielsen and Romano-ward Forms of Long Qt Syndrome in a Chinese Family

Background: Long QT syndrome (LQTS) is a cardiac disorder characterized by prolonged QT intervals on electrocardiograms (ECG), ventricular arrhythmias, and sudden death. Clinically, two inherited forms of LQTS have been defined: autosomal dominant LQTS or Romano-Ward syndrome (RWS) not associated with deafness and autosomal recessive LQTS or Jervell and Lange-Nielsen syndrome (JLNS) associated with deafness.


Background
Long QT syndrome (LQTS) is a disorder of cardiac repolarization characterized by prolonged QT intervals and abnormal T waves on surface electrocardiograms (ECG), torsade de pointes, and sudden death [1][2][3]. Two forms of inherited LQTS have been described: Romano-Ward syndrome (RWS), which is an autosomal dominant form of LQTS without sensorineural deafness, and Jervell and Lange-Nielsen syndrome (JLNS), which is an autosomal recessive form of LQTS associated with deafness [4][5][6].
In this report, we identified a novel mutation in the KCNQ1 gene that simultaneously caused RWS and JLNS within a Chinese family. The results expand the spectrum of KCNQ1 mutations causing RWS and JLNS.

Results
One three-generation JLN/RWS family was identified in China and clinically evaluated. The pedigree structure of the family is shown in Figure 1, and clinical characteristics for family members are listed in Table 1. The proband (patient III:1) had been deaf since birth. At 3 years of age, she was referred for detailed examinations due to syncope. Since then, she has experienced 11 additional syncopal episodes, most of which were preceded by exercise and sport. Current ECG analysis revealed a markedly prolonged QTc ranging from 0.520 to 0.608 s (a representative ECG is shown in Figure 2). She was then diagnosed as having JLNS (deafness + LQTS). Interestingly, the proband was also affected with atrial fibrillation. The proband's brother (patient III:2, Figure 1) was also affected with deafness and LQTS (JLNS). His QTc ranged from 0.512 s to 0.627 s, and he had experienced three syncopal episodes in the past triggered by exercise and sport. Their parents had normal hearing and normal ECGs with a QTc of 0.42 s (father) and 0.43 s (mother). Individual II:1 had experienced one syncopal episode triggered by exercise when she was 20 years old. No syncope was identified for individual II:2, but he had experienced palpitation and dyspnea. The parents' marriage was not consanguineous.
Further analysis of other family members identified two other members affected with RWS. Individual II:4 was clinically diagnosed with LQTS because she had a moderately prolonged QTc of 0.455 s and a medical history of dyspnea and palpitation. Her mother (I:2, Figure 1) was also affected with LQTS with a prolonged QTc of 0.487 s. Both I:2 and II:4 had normal hearing. Individual III:4 was a male with a borderline QTc of 0.447 s. No stress testing was performed for III:4 or other family members. Individuals I:1, II:3, and III:3 had a normal QTc of 0.420 s, 0.400 s, and 0.397 s, respectively.
A homozygous C → T transition was identified at nucleotide 965 in exon 7 of KCNQ1 in the DNA sample from the proband (Figure 3). The C to T change resulted in the substitution of a threonine residue by a methionine residue at codon 322 (T322M) (Figure 3). The homozygous T322M mutation was also identified in the proband's brother (individual III:2, Figure 1). The parents and family members II:4 and I:2 were heterozygous for the mutation.
The detection of mutation T322M was further confirmed by RFLP analysis showing the presence of only the mutant allele (M322) in the proband and her brother ( Figure 1, Table 1). RFLP analysis also demonstrated that family members II:1, II:2, I:2, II:4, and III:4 were heterozygous for the mutation (T322 and M322) and that normal individuals I:1, II:3, and III:3 carried the wild type T322 allele. The M322 allele was not identified in 200 normal Chinese Han nationality controls (data not shown).

Discussion
In this report, we describe a Chinese family in which a heterozygous mutation in KCNQ1, T322M, resulted in RWS whereas the homozygous mutation resulted in JLNS associated with LQTS and deafness. Heterozygous mutations in the KCNQ1 gene have been reported in Chinese patients with RWS, but no KCNQ1 mutation associated with JLN has been reported in the Chinese population [29]. Thus, the T322M is the first KCNQ1 mutation identified for JLN in the Chinese population.
The penetrance of the phenotype in the family members with homozygous T322M was complete. The two homozygous mutation carriers, III:1 and III:2 (Figure 1), had a markedly prolonged QTc of up to 0.608 s and 0.627 s, respectively, and both had experienced multiple syncopal episodes triggered by exercise and sport. These results are consistent with the finding by Schwartz et al. [24] that JLN is a more severe variant of LQTS than RWS. Interestingly, individual III:1 was affected by both LQTS and atrial fibrillation. Previously, in a Chinese family with atrial fibrillation and KCNQ1 mutation S140G, multiple family members had both LQTS and atrial fibrillation [30]. Further studies are needed to determine whether and how the T322M mutation is associated with atrial fibrillation.
The penetrance of the phenotype of QTc prolongation in heterozygous mutation carriers was not complete. Two carriers, II-1 and II-2, had a normal QTc (Table 1, Figure  1). On the other hand, two carriers, I-2 and II:4, were affected with RWS. The other carrier, III-4, had borderline QTc prolongation. The molecular mechanism that is responsible for the intra-familial variability or variable penetrance of the LQTS phenotype in heterozygous carriers is not clear, but environmental factors and modifying genes are likely possibilities.

Conclusion
This study identified a novel mutation, T322M, in the KCNQ1 gene that caused RWS with high intrafamilial variability in the heterozygous carriers and typical JLNS in the homozygous carriers within a Chinese family. To the best of our knowledge, T322M is the first mutation identified for JLNS in the Chinese population.

Study subjects, clinical diagnosis, and isolation of human genomic DNA
The LQTS family was identified in the Henan Province of China. Informed consent was obtained from all the participants or their guardians. This study complied with the Helsinki Declaration and was approved by the ethics committee of Huazhong University of Science and Technology.
LQTS was diagnosed based on the presence of prolonged QT intervals as seen on a 12-lead ECG and a medical history of syncope, dyspnea, and palpitation. The QT interval was manually measured, and the QTc was calculated using Bazett's formula for heart rate correction [31]. The diagnosis of LQTS was based on the work of Schwartz et al. [32] and others [8,10,11]. Asymptomatic individuals with a QTc of ≥ 0.47 s and symptomatic individuals (syncope, dyspnea, palpitation) with a QTc ≥ 0.45 s were diagnosed with LQTS. Males with a QTc of <0.44 s and females with a QTc of <0.45 s were considered normal. All others were diagnosed as having borderline QTc.
Peripheral blood was collected from the participants, and their total human genomic DNA was isolated using the DNA Isolation Kit for Mammalian Blood (Roche Diagnostic Co., Indianapolis, IN).

Competing interests
The author(s) declare that they have no competing interests.

Authors' contributions
SZ recruited the patients and family and performed the clinical and genetic studies and data analysis. KY performed genetic and clinical studies and data analysis, interpreted the results, and drafted the manuscript. XR participated in the experimental design, data analysis, interpretation of results, and supervision of the project. PW participated in genetic studies. SZ participated in genetic studies and data analysis. LC assisted with the recruitment of the patients and family and analysis of the clinical data. JY participated in the analysis of the clinical data. JYL participated in data analysis and interpretation of genetic results. ML participated in the experimental design, data analysis, interpretation of results, and supervision of the project. ML also obtained funding and helped draft the manuscript. QKW participated in the experimental design, analysis of genetic data, interpretation of the results, analysis of clinical data, and supervision of the project, obtained funding, drafted the manuscript, and critically revised the Figures, Table and entire manuscript. All authors approved the final manuscript.