对一个遗传上难以捉摸的多代长 QT 综合征家系进行基因组测序，鉴定出一种新的 LQT2 致病的深内含子 KCNH2 变异。
Genome sequencing in a genetically elusive multigenerational long QT syndrome pedigree identifies a novel LQT2-causative deeply intronic KCNH2 variant.
机构信息
Department of Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, Minnesota.
Department of Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, Minnesota; Department of Cardiovascular Medicine, Division of Heart Rhythm Services, Windland Smith Rice Genetic Heart Rhythm Clinic, Mayo Clinic, Rochester, Minnesota.
出版信息
Heart Rhythm. 2022 Jun;19(6):998-1007. doi: 10.1016/j.hrthm.2022.02.004. Epub 2022 Feb 7.
BACKGROUND
Most of the long QT syndrome (LQTS) stems from pathogenic variants in KCNQ1, KCNH2, or SCN5A. However, ∼10%-20% of LQTS index cases remain genotype-negative.
OBJECTIVE
The purpose of this study was to identify and characterize functionally a novel LQTS genetic substrate in a multigenerational, "genotype-negative" LQTS pedigree.
METHODS
The patient was a 40-year-old woman with a history of syncope, seizures, ventricular fibrillation, and a family history of LQTS and sudden death. Commercial genetic testing of all LQTS-causative genes was negative. Genome sequencing was performed on 6 affected family members. Patient-specific and CRISPR/Cas9 "gene-corrected" isogenic control induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were generated.
RESULTS
No ultrarare, nonsynonymous heterozygous variants cosegregated among the 6 LQTS phenotype-positive individuals. Instead, a deep intronic KCNH2 variant (c.3331-316G>T) was present in all affected individuals. Reverse transcription polymerase chain reaction analysis of patient-specific iPSC-CM-derived RNA revealed that c.3331-316G>T creates a novel 89 base-pair exon that results in a frameshift variant (p.S1112Pfs∗171). Action potential duration (APD) was significantly longer in p.S1112Pfs∗171-iPSC-CMs (602.4 ± 12.2 ms; n =70) compared to isogenic control iPSC-CMs (425.7 ± 9.3 ms; n = 61; P <.0001). Further, field potential duration was significantly longer in p.S1112Pfs∗171-iPSC-CMs (358.9 ± 7.7 ms; n = 65) compared to isogenic control iPSC-CMs (282.2 ± 10.8 ms; n = 51; P <.0001).
CONCLUSION
A novel deep intronic KCNH2 variant was identified in a multigenerational, genetically elusive LQTS pedigree. The iPSC-CMs establish that the variant is the monogenetic cause for this family's LQTS. Deep intronic variants within the 2 most common LQTS-susceptibility genes should be considered in patients with seemingly genetically elusive LQTS.
背景
大多数长 QT 综合征（LQTS）源自 KCNQ1、KCNH2 或 SCN5A 的致病性变异。然而，约 10%-20%的 LQTS 索引病例仍为基因型阴性。
目的
本研究旨在鉴定和描述一个多代、“基因型阴性”LQTS 家系中一种新的 LQTS 遗传底物，并对其进行功能分析。
方法
患者为 40 岁女性，有晕厥、癫痫发作、心室颤动病史，并有 LQTS 和猝死家族史。对所有 LQTS 致病基因进行商业基因检测均为阴性。对 6 名受影响的家族成员进行基因组测序。生成患者特异性和 CRISPR/Cas9“基因纠正”同源诱导多能干细胞衍生心肌细胞（iPSC-CM）。
结果
在 6 名 LQTS 表型阳性个体中，没有超罕见、非同义杂合变体共分离。相反，在所有受影响的个体中均存在深内含子 KCNH2 变体（c.3331-316G>T）。患者特异性 iPSC-CM 衍生 RNA 的逆转录聚合酶链反应分析显示，c.3331-316G>T 产生了一个新的 89 个碱基对的外显子，导致移码变异（p.S1112Pfs∗171）。p.S1112Pfs∗171-iPSC-CM 的动作电位时程（APD）明显长于同基因对照 iPSC-CM（602.4±12.2 ms；n=70）（425.7±9.3 ms；n=61；P<.0001）。进一步，p.S1112Pfs∗171-iPSC-CM 的场电位时程（358.9±7.7 ms；n=65）明显长于同基因对照 iPSC-CM（282.2±10.8 ms；n=51；P<.0001）。
结论
在一个多代、遗传上难以捉摸的 LQTS 家系中发现了一种新型深内含子 KCNH2 变体。iPSC-CM 证实该变体是该家系 LQTS 的单基因原因。在看似遗传上难以捉摸的 LQTS 患者中，应考虑 2 个最常见的 LQTS 易感性基因内的深内含子变异。
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