For instance, Legius syndrome, which is caused by the RAS/MAPK-member SPRED1’s pathogenic variation, behaves as an AD genetic disorder, even though the protein encoded by that gene acts as a tumor suppressor in a homo-, or heterodimer with its paralog Sprouty Related EVH1 Domain Containing 2 (SPRED2). Here, SPRED1 is linked to Legius syndrome.