Protective effect of KCNH2 single nucleotide polymorphism K897T in LQTS families and identification of novel KCNQ1 and KCNH2 mutations

Abstract

Background: KCNQ1 and KCNH2 are the two most common potassium channel genes causing long QT syndrome (LQTS), an inherited cardiac arrhythmia featured by QT prolongation and increased risks of developing torsade de pointes and sudden death. To investigate the disease expressivity, this study aimed to identify mutations and common variants that can modify LQTS phenotype.

Methods: In this study, a cohort of 112 LQTS families were investigated. Among them two large LQTS families linkage analysis with markers spanning known LQTS genes was carried out to identify the specific gene for mutational analysis. All exons and exon-intron boundaries of KCNH2 and KCNQ1 were sequenced for mutational analysis.

Results: LQTS-associated mutations were identified in eight of 112 families. Two novel mutations, L187P in KCNQ1 and 2020insAG in KCNH2, were identified. Furthermore, in another LQTS family we found that KCNH2 mutation A490T co-segregated with a common SNP K897T in KCNH2. KCNH2 SNP K897T was reported to exert a modifying effect on QTc, but it remains controversial whether it confers a risk or protective effect. Notably, we have found that SNP K897T interacts with mutation A490T in cis orientation. Seven carriers for A490T and the minor allele T of SNP K897T showed shorter QTc and fewer symptoms than carriers with A490T or A490P (P < 0.0001).

Conclusion: Our family-based approach provides support that KCNH2 SNP K897T confers a protective effect on LQTS patients. Our study is the first to investigate the effect of SNP K897T on another KCNH2 mutation located in cis orientation. Together, our results expand the mutational and clinical spectrum of LQTS and provide insights into the factors that determine QT prolongation associated with increased risk of ventricular tachycardia and sudden death.

Figure 1

Identification and co-segregation of KCNH2 mutation A490T and SNP K897T in family QW2648 and with LQTS. (A). Pedigree structure of family QW2648. All the affected individuals carry double variants, K897T and A490T of KCNH2 on the same chromosome (in cis orientation). (B, C). DNA sequence analysis for the proband in family QW2648. A heterozygous G→A transition at nucleotide 1468 of KCNH2, which results in a substitution of alanine by threonine (A490T) (B). DNA sequence for KCNH2 SNP K897T is shown in (C). (D) Comparison of mean QTc for carriers with KCNH2 mutation A490T, A490P, and both A490T and SNP K897T.

Figure 2

Identification of a novel mutation, L187P, in KCNQ1 in LQTS family QW1648. (A). A partial pedigree structure for the large Utah family is shown. The family had over 300 members. For ease of illustration only a portion of the pedigree is shown. Affected males and females are indicated by filled squares and circles, respectively. Normal individuals are shown as empty symbols. Individuals with uncertain LQTS diagnosis are shown with gray symbols. Deceased individuals are shown using slashes. The identification numbers for family members and QTc are shown below symbols. (B). DNA sequence analysis revealed a heterozygous T→C transition at nucleotide 560 of KCNQ1, which results in a substitution of amino acid residue leucine by a proline residue (L187P). The sequence for a normal family member is shown on the top and the sequence for an affected family member is shown below. (C). SSCP analysis showed co-segregation of the mutation L187P with the LQTS phenotype in the family. All phenotypically affected members had two bands, and the non-affected individuals had only one band.

Figure 3

(A) Reduced penetrance of LQTS phenotype and effect of exercise on QTc. Mean QTc for carriers with mutation L187P and 11 non-carriers (left) and mean QTc for mutation carriers before (resting state) and during exercise (right). (B, C) Example of reduced penetrance of LQTS phenotype at baseline. Initial ECG (B) and ECG after 15-min exercise (C) are shown for a 29 year old, male, asymptomatic mutation L187P carrier.

Figure 4

Identification of a novel mutation in KCNH2, 2020insAG, in family QW258. Top, pedigree structure; Middle, DNA sequence for the patient using the forward primer; Bottom, DNA sequence for the patient using the reverse primer.