Irrespective of the associated phenotypes, a common feature of all CaM mutations identified so far is the extreme severity of disease manifestations and early occurrence with almost half of subjects having a perinatal presentation (28th week of gestation to 28th postnatal day) (12/28, 43%, with the exclusion of 2 SUDs), mainly among those with an LQTS phenotype. Here, CALM1 is linked to familial long QT syndrome.