POLR1C and Familial progressive cardiac conduction defect: In another family, quad WES analysis identified a paternally inherited heterozygous missense variant of unknown significance in SCN1B, the gene for Brugada syndrome 5 (MIM 612838) [73], and compound heterozygous changes in POLR1C, segregating in two affected siblings (Table 1, Additional file 3: Table S2, Additional file 4: Supplemental text).