CALR and atrioventricular block: The incidence of atrioventricular block (AVB) is of 1 per 15,000–20,000 live births, and 50% to 55% of these cases are caused by the presence of structural congenital heart disease.1 In total, 40% of AVBs are mainly related to SSA/Ro- or SSB/La-positive maternal antibodies.