KRAS and Costello syndrome: Other effects, such as the preferential expression of isoforms during development or even different localisation dynamics (Chandra et al, 2012), should be taken into account to explain why Costello syndrome mutations that harbour a G12X mutation in HRAS do not show up frequently in cancer (although Costello syndrome patients do develop tumours more frequently; Gripp & Lin, 2012), while KRAS G12X mutations are frequently involved in cancer.