Novel CALM3 Variant Causing Calmodulinopathy With Variable Expressivity in a 4-Generation Family
Novel CALM3 Variant Causing Calmodulinopathy With Variable Expressivity in a 4-Generation Family
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DOI：
10.1161/circep.121.010572
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发表时间：
2022-03-01
影响因子：
8.4
通讯作者：
Guicheney, Pascale
中科院分区：
文献类型：
--
作者：
Kato, Koichi;Isbell, Holly M.;Guicheney, Pascale
背景：钙调蛋白（CaM）由3个独立基因（CALM1、CALM2和CALM3）编码，是一种多功能的钙离子结合蛋白，参与包括离子通道调节在内的多种信号转导过程。钙调蛋白变异体可能导致早发性长QT综合征（LQTS）、儿茶酚胺能多形性室性心动过速或心源性猝死。大多数已报道的变异体为新生突变。我们在一个LQTS呈四代遗传的家系中发现了一种新的CALM3变异体p.Asn138Lys（N138K）。本研究旨在阐明其致病性，并将其与与严重LQTS表型相关的p.D130G - CaM变异体进行比较。
方法：我们对一个受LQTS影响的四代大家系进行了全外显子测序。为评估检测到的CALM3变异体的影响，通过化学计量钙离子滴定和平衡滴定测量内在钙离子结合亲和力。采用全细胞膜片钳记录L型钙电流和缓慢延迟整流钾电流（I - CaL和I - Ks）。通过光学荧光测定法确定Cav1.2和Kv7.1的膜表达情况。
结果：我们在一个家系中鉴定出14名p.N138K - CaM携带者，该家系中有2名儿童发生猝死。与文献中迄今描述的CaM - LQTS患者相比，该家系的几名成员仅受到轻度影响。与野生型CaM相比，p.N138K - CaM的CaM C末端结构域的内在钙离子结合亲和力低10倍。在表达p.N138K - CaM的细胞中，I - CaL失活减慢，但比表达p.D130G - CaM的细胞程度轻。出乎意料的是，与野生型CaM相比，在表达p.N138K - CaM的细胞中观察到更大的I - Ks电流密度，而表达p.D130G - CaM的细胞则没有。
结论：p.N138K CALM3变异体损害CaM的钙离子结合亲和力和I - CaL失活，但增强I - Ks。与先前发表的新生LQTS - CaM变异体相比，该变异体表现出的可变表型，很可能是由于I - CaL失活的较轻损害与I - Ks增强共同作用所致。
Background: CaM (calmodulin), encoded by 3 separate genes (CALM1, CALM2, and CALM3), is a multifunctional Ca2+-binding protein involved in many signal transduction events including ion channel regulation. CaM variants may present with early-onset long QT syndrome (LQTS), catecholaminergic polymorphic ventricular tachycardia, or sudden cardiac death. Most reported variants occurred de novo. We identified a novel CALM3 variant, p.Asn138Lys (N138K), in a 4-generation family segregating with LQTS. The aim of this study was to elucidate its pathogenicity and to compare it with that of p.D130G-CaM-a variant associated with a severe LQTS phenotype. Methods: We performed whole exome sequencing for a large, 4-generation family affected by LQTS. To assess the effect of the detected CALM3 variant, the intrinsic Ca2+-binding affinity was measured by stoichiometric Ca2+ titrations and equilibrium titrations. L-type Ca2+ and slow delayed rectifier potassium currents (I-CaL and I-Ks) were recorded by whole-cell patch-clamp. Cav1.2 and Kv7.1 membrane expression were determined by optical fluorescence assays. Results: We identified 14 p.N138K-CaM carriers in a family where 2 sudden deaths occurred in children. Several members were only mildly affected compared with CaM-LQTS patients to date described in literature. The intrinsic Ca2+-binding affinity of the CaM C-terminal domain was 10-fold lower for p.N138K-CaM compared with wild-type-CaM. I-CaL inactivation was slowed in cells expressing p.N138K-CaM but less than in p.D130G-CaM cells. Unexpectedly, a larger I-Ks current density was observed in cells expressing p.N138K-CaM, but not for p.D130G-CaM, compared with wild-type-CaM. Conclusions: The p.N138K CALM3 variant impairs Ca2+-binding affinity of CaM and I-CaL inactivation but potentiates I-Ks. The variably expressed phenotype of this variant compared with previously published de novo LQTS-CaM variants is likely explained by a milder impairment of I-CaL inactivation combined with I-Ks augmentation.