Novel calmodulin mutations associated with congenital long QT syndrome affect calcium current in human cardiomyocytes

Pipilas, D. C.; Johnson, C. N.; Webster, G.; Schlaepfer, J.; Fellmann, F.; Sekarski, N.; Wren, L. M.; Ogorodnik, K. V.; Chazin, D. M.; Chazin, W. J.; Crotti, L.; Bhuiyan, Z. A.; George, A. L., Jr.

Heart Rhythm. 2016 Jul 5; 13(10):2012-9

Abstract

BACKGROUND: Calmodulin (CaM) mutations are associated with cardiac arrhythmia susceptibility including congenital long QT syndrome (LQTS). OBJECTIVE: The purpose of this study was to determine the clinical, genetic, and functional features of 2 novel CaM mutations in children with life-threatening ventricular arrhythmias. METHODS: The clinical and genetic features of 2 congenital arrhythmia cases associated with 2 novel CaM gene mutations were ascertained. Biochemical and functional investigations were conducted on the 2 mutations. RESULTS: A novel de novo CALM2 mutation (D132H) was discovered by candidate gene screening in a male infant with prenatal bradycardia born to healthy parents. Postnatal course was complicated by profound bradycardia, prolonged corrected QT interval (651 ms), 2:1 atrioventricular block, and cardiogenic shock. He was resuscitated and was treated with a cardiac device. A second novel de novo mutation in CALM1 (D132V) was discovered by clinical exome sequencing in a 3-year-old boy who suffered a witnessed cardiac arrest secondary to ventricular fibrillation. Electrocardiographic recording after successful resuscitation revealed a prolonged corrected QT interval of 574 ms. The Ca(2+) affinity of CaM-D132H and CaM-D132V revealed extremely weak binding to the C-terminal domain, with significant structural perturbations noted for D132H. Voltage-clamp recordings of human induced pluripotent stem cell-derived cardiomyocytes transiently expressing wild-type or mutant CaM demonstrated that both mutations caused impaired Ca(2+)-dependent inactivation of voltage-gated Ca(2+) current. Neither mutant affected voltage-dependent inactivation. CONCLUSION: Our findings implicate impaired Ca(2+)-dependent inactivation in human cardiomyocytes as the plausible mechanism for long QT syndrome associated with 2 novel CaM mutations. The data further expand the spectrum of genotype and phenotype associated with calmodulinopathy.

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