FGFR2 and Pfeiffer syndrome: The ECD mutations W290G or T341P within FGFR-2, which are directly linked to the initiation of Crouzon and Pfeiffer syndromes, release a free cysteine by disrupting a nearby intramolecular disulfide bond, triggering intermolecular bonding, activation and conferring tumorigenic properties in NIH3T3 cells [25].