PCDH19 and developmental and epileptic encephalopathy: The overall estimated annual incidence of single-gene epilepsies in this population was 1 per 2120 live births (47.2/100 000; 95% CI 36.9 to 57.5), with pathogenic variants in SCN1A, PCDH19, CDKL5 and KCNQ2, having the highest incidence for DEE.