Cognitive impairment ranging from mild to severe is one of the core symptoms of PCDH19-CE.3,5,2,49,50 Thus, we hypothesized that a defective development of the hippocampus (as one of the main brain regions involved in learning and memory51) by PCDH19 downregulation may contribute to the cognitive impairment present in PCDH19-CE. The gene discussed is PCDH19; the disease is Cognitive impairment.