LQTS-associated calmodulinopathies are due to a mutation occurring in one of the 3 calmodulin genes, CALM1, CALM2, and CALM3. In this work, the proband affected by the malignant calmodulinopathic long QT syndrome harbored a mutation in only 1 of 6 redundant calmodulin-encoding alleles. This evidence concerns the gene CALM2 and familial long QT syndrome.