MAPK1 and Legius syndrome: As summarized in Table 1, mouse models for Costello Syndrome (CS), Neurofibromatosis I (NF1), Noonan Syndrome (NS), and Legius Syndrome show similar phenotypes including hyperactivity of the RAS-ERK pathway, learning deficits in the water maze, and impaired synaptic plasticity, which confirm the widespread observation of overlapping disease manifestations across patients with different RASopathies.