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). Here, PCDH19 is linked to X-linked intellectual disability - epilepsy.