Genetic Mosaicism in Calmodulinopathy.

Abstract

Background - Calmodulin (CaM) mutations are associated with congenital arrhythmia susceptibility (calmodulinopathy) and are most often de novo. In this report, we sought to broaden the genotype-phenotype spectrum of calmodulinopathies with two novel calmodulin mutations, and to investigate mosaicism in two affected families. Methods - CaM mutations were identified in four independent cases by DNA sequencing. Biochemical and electrophysiological studies were performed to determine functional consequences of each mutation. Results - Genetic studies identified two novel CaM variants (CALM3-E141K in two cases; CALM1-E141V) and one previously reported CaM pathogenic variant (CALM3-D130G) among four probands with shared clinical features of prolonged QTc interval (range 505 - 725 ms) and documented ventricular arrhythmia. A fatal outcome occurred for two of the cases. The parents of all probands were asymptomatic with normal QTc duration. However, two of the families had multiple affected offspring or multiple occurrences of intrauterine fetal demise (IUFD). The mother from the family with recurrent IUFD exhibited the CALM3-E141K mutant allele in 25% of next-generation sequencing reads indicating somatic mosaicism, whereas CALM3-D130G was present in 6% of captured molecules of the paternal DNA sample, also indicating mosaicism. Two novel mutations (E141K, E141V) impaired Ca2+ binding affinity to the C-domain of CaM. Human induced pluripotent stem cell (iPSC) derived cardiomyocytes overexpressing mutant or WT CaM showed that both mutants impaired Ca2+-dependent inactivation (CDI) of L-type Ca2+ channels (LTCC) and prolonged action potential duration. Conclusions- We report two families with somatic mosaicism associated with arrhythmogenic calmodulinopathy, and demonstrate dysregulation of the LTCC by two novel CaM mutations affecting the same residue. Parental mosaicism should be suspected in families with unexplained fetal arrhythmia or fetal demise combined with a documented CaM mutation.