POPDC2 and hypertrophic cardiomyopathy: Here, we provide evidence for bi-allelic loss-of-function (LOF) variants in POPDC2 as the cause of an autosomal recessive syndrome in four families, consisting of a phenotypic spectrum including sinus node disease and AV conduction defects with hypertrophic cardiomyopathy (HCM; MIM: 192600).