NS is part of a clinical spectrum of conditions which include Noonan‐like disorders due to mutations in SHOC2, PPP1CB and CBL, Costello syndrome caused by HRAS mutations and cardiofaciocutaneous syndrome caused by disruption of BRAF, MAP2K1 and MAP2K2. These disorders all result from dysregulation of RAS‐MAPK signalling so have collectively been termed the “RASopathies”. This evidence concerns the gene MAP2K2 and Costello syndrome.