Clinically, genetic variants in PCDH19 have been linked to a rare newly individualized syndrome: epilepsy in females with mental retardation (EFMR), also known as early infantile epileptic encephalopathy (EIEE9) or PCDH-19 clustering epilepsy (OMIM #300088), and in fact comes second in the list of genes associated with this disease [31,32]. The gene discussed is PCDH19; the disease is early-infantile DEE.