EPAS1 and Costello syndrome: Whilst HIF2A mutations may be found in multiple tumours from patients without a detectable germline mutation (suggesting low level constitutional mosaicism) or occasionally as a germline mutation [5], to date HRAS mutations have only been detected as somatic changes (germline HRAS mutations are associated with Costello syndrome but PCC/PGL/HNPGL are apparently not a feature of this disorder) [34].