Identification of KCNQ1 compound heterozygous mutations in three Chinese families with Jervell and Lange-Nielsen Syndrome

Clinical Heterogeneity in Patients with Long QT Syndrome and Segregation of Single Nucleotide Variants and Clinical Symptoms in 17 Affected Families

Introduction

Long QT syndrome (LQTS) is a disorder of ventricular myocardial repolarization characterized by a prolonged QT interval on the electrocardiogram. It increases the risk of ventricular arrhythmias, which can cause syncope or sudden cardiac death. In this study, we study the genotype-phenotype relationships of patients referred to us with suspected arrhythmia syndrome.

Methods

Seventeen cases and their twenty relatives were evaluated. Next-generation sequencing analysis was performed for 17 LQTS-related genes.

Results

We detected seventeen single nucleotide variants (SNVs) with potential pathogenic significance in 26 of the 36 subjects analyzed. KCNH2 c.172G>A, KCNQ1 c.1768G>A, ANK2 c.4666A>T, c.1484_1485delCT, KCNH2 c.1888G>A were reported as pathogenic or likely pathogenic in HGMD variant classification database.

Conclusion

Current study pointed out that early diagnosis can be life-saving for patients and their families by taking family history and detailed examination. Also, we highlight the clinical heterogeneity of arrhythmia syndrome through a patient with a dual phenotype.

Eosinophilic Infiltration of the Sino-Atrial Node in Sudden Cardiac Death Caused by Long QT Syndrome

Sudden death is defined as the unexpected death of a healthy person that occurs within the first hour of the onset of symptoms or within 24 h of the victim being last seen alive. In some of these cases, rare deleterious variants of genes associated with inherited cardiac disorders can provide a highly probable explanation for the fatal event. We report the case of a 21-year-old obese woman who lost consciousness suddenly in a public place and was pronounced dead after hospital admission. Clinical autopsy showed an inconclusive gross examination, while in the histopathological analysis an eosinophilic inflammatory focus and interstitial fibrosis in the sino-atrial node were found. Molecular autopsy revealed an intronic variant in the KCNQ1 gene (c.683 + 5G > A), classified as likely pathogenic for long QT syndrome according to the guidelines provided by the American College of Medical Genetics and Genomics. Therefore, there were many anomalies that could have played a role in the causation of the sudden death, such as the extreme obesity, the cardiac anomalies and the KNCQ1 variant. This case depicts the difficult interpretation of rare cardiac structural abnormalities in subjects carrying rare variants responsible for inherited arrhythmic disorders and the challenge for the forensic pathologist to make causal inferences in the determinism of the unexpected decease.

The Pathological Mechanisms of Hearing Loss Caused by KCNQ1 and KCNQ4 Variants

Deafness-associated genes KCNQ1 (also associated with heart diseases) and KCNQ4 (only associated with hearing loss) encode the homotetrameric voltage-gated potassium ion channels Kv7.1 and Kv7.4, respectively. To date, over 700 KCNQ1 and over 70 KCNQ4 variants have been identified in patients. The vast majority of these variants are inherited dominantly, and their pathogenicity is often explained by dominant-negative inhibition or haploinsufficiency. Our recent study unexpectedly identified cell-death-inducing cytotoxicity in several Kv7.1 and Kv7.4 variants. Elucidation of this cytotoxicity mechanism and identification of its modifiers (drugs) have great potential for aiding the development of a novel pharmacological strategy against many pathogenic KCNQ variants. The purpose of this review is to disseminate this emerging pathological role of Kv7 variants and to underscore the importance of experimentally characterizing disease-associated variants.

Identification of a complex genomic rearrangement in TMPRSS3 by massively parallel sequencing in Chinese cases with prelingual hearing loss

BACKGROUND

Genetic variants in TMPRSS3 have been causally linked to autosomal recessive nonsyndromic hearing loss (HL) at the DFNB8 and DFNB10 loci. These variants include both single nucleotide and copy number variations (CNVs). In this study, we aim to identify the genetic cause in three Chinese subjects with prelingual profound sensorineural HL.

METHODS

We applied targeted genomic enrichment and massively parallel sequencing to screen 110 genes associated with nonsyndromic HL in the three affected subjects. CNVplex^® analysis and polymerase chain reaction (PCR) were performed for CNV detection.

RESULTS

We identified biallelic variations in TMPRSS3 including a novel complex genomic rearrangement and a novel missense mutation, c.551T>C. We have mapped the breakpoints of the genomic rearrangement and showed that it consisted of two deletions and an inversion encompassing exon 3 to exon 9 of TMPRSS3.

CONCLUSION

Our study expanded the mutational spectrum of TMPRSS3 to include complex genomic rearrangements. It showcased the importance of an integrative approach to investigate CNVs and their contribution to HL.

Hypermethylated KCNQ1 acts as a tumor suppressor in hepatocellular carcinoma

Potassium (K⁺) channels are dysregulated in tumor tissues and functionally these channels contribute significantly to the malignant phenotypes of the cancer cells, including cell apoptosis, chemo- and radio-resistance, proliferation, and migration. However, little is known about the potential implications of K⁺ channels in hepatocellular carcinoma (HCC). The aim of the current study was to investigate the expression profile of KCNQ1 in HCC and assess its possible cellular implications as well as mechanism to disease progression. Using real-time qPCR and western blotting technique, we found that KCNQ1 was frequently down-regulated in HCC cell lines and tissues, and HCC patients with lower KCNQ1 expression had a poor prognosis. Specifically, DNA hypermethylation of KCNQ1 promoter resulted in its downregulation in HCC. Bioinformatic analysis indicated a regulatory role of KCNQ1 in the epithelial-to-mesenchymal transition process. Gain-of-function study showed that KCNQ1 exhibited remarkable inhibitory roles on tumor metastasis in vitro and in vivo. Mechanistically, KCNQ1 can interact with β-catenin to affect its subcellular distribution and subsequently reduce the activity of Wnt/β-catenin signaling, which further blocks the expression of its downstream targets, including c-Myc, MMP7, and CCND1. Restoration of β-catenin activity largely compromised the tumor-suppressive roles of KCNQ1 in the invasive capacity of HCC cells. In conclusion, KCNQ1 is down-regulated in HCC and may suppress HCC metastasis, which could represent a prognostic marker and promising therapeutic target for HCC.