PCDH19-Clustering Epilepsy (PCE), formally known as developmental and epileptic encephalopathy-9 (DEE9), is caused by pathogenic variants in Protocadherin-19 (PCDH19), an X-chromosome gene that undergoes random X-inactivation (RXI) (Dibbens et al., 2008; Kolc et al., 2019). The gene discussed is PCDH19; the disease is developmental and epileptic encephalopathy, 9.