Novel CALM3 Variant Causing Calmodulinopathy With Variable Expressivity in a 4-Generation Family

Abstract

Background: CaM (calmodulin), encoded by 3 separate genes ( CALM1 , CALM2 , and CALM3 ), is a multifunctional Ca 2+ -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 Ca 2+ -binding affinity was measured by stoichiometric Ca 2+ titrations and equilibrium titrations. L-type Ca 2+ 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 Ca 2+ -binding affinity of the CaM C-terminal domain was 10-fold lower for p.N138K-CaM compared with WT-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 WT-CaM. Conclusions: The p.N138K CALM3 variant impairs Ca 2+ -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.

Case report: Prenatal diagnosis of fetal non-compaction cardiomyopathy with bradycardia accompanied by de novo CALM2 mutation

“…However, involvement of the calmodulin gene ( CALM2 ) in fetal NCCM has been rarely reported. CALM2 is a Ca 2+ -signaling gene that encodes for calmodulin, which is a multifunctional Ca 2+ -binding protein ( 4 ). Calmodulin is also an important calcium-sensitive signal transduction protein involved in regulating almost every cardiac ion channel through calcium/calmodulin-dependent protein kinase II ( 5 , 6 ), and calmodulin may simultaneously contribute to cardiomyopathy and arrhythmia.…”

Calmodulin variant E140G associated with long QT syndrome impairs CaMKIIδ autophosphorylation and L-type calcium channel inactivation

“…More than 90% of genetically confirmed cases of LQTS can be linked to mutations in potassium (K + ) or sodium (Na + ) channels ( 4 , 5 , 6 ). However, mutations in the highly conserved calcium (Ca 2+ )-sensing protein, calmodulin (CaM), have recently been implicated in LQTS ( 5 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ). CaM variant–mediated LQTS present different disease severities and this phenotypic presentation may be regulated by distinct underlying mechanisms.…”

Precision medicine for long QT syndrome: patient-specific iPSCs take the lead

“…86). Patients with LQTS were shown to have a variety of mutations (D130G, F142L and E141 G in CALM1; D96 V, N98I, N98S, D130G, D130 V, D132E, D134H and Q136P in CALM2; and D130 G and N138 K in CALM3) (Refs 86, 87, 88). Most mutations are located in calmodulin's C-terminal Ca2 + -binding domains (EF-hands III and IV), particularly in the residues directly involved in Ca2 + binding.…”

“…Most mutations are located in calmodulin's C-terminal Ca2 + -binding domains (EF-hands III and IV), particularly in the residues directly involved in Ca2 + binding. A plethora of evidence indicate that LQTS relevant calmodulin mutations attenuate Ca2 + binding affinity and result in a defective Ca2 + -dependent inactivation of Cav1.2, causing an increased and uncontrolled Ca2 + influx (Refs 88, 89). The mutation locations in CALM1-3 reveals special topological domains that are susceptible to genetic variation and imply the significance of Ca2 + -binding affinity for proper function of calmodulin.…”