To characterize the NE phenotypes further, we obtained CS patient-derived cell lines carrying loss-of-function mutations causing destabilization of CSA and CSB in CSA (CS-A cells) or CSB (CS-B cells), respectively (6), and their respective isogenic control cell lines WT(HA-CSA) and WT(HA-GFP-CSB) (37). The gene discussed is ERCC8; the disease is Cowden syndrome 1.