FGFR2 and Pfeiffer syndrome: Apert and Crouzon syndromes are caused by mutations in FGFR2 that increase affinity of the receptor for the ligand, and Pfeiffer syndrome is caused by mutations in either FGFR2 or FGFR1 (Schell et al., 1995; Anderson et al., 1998; Hibberd et al., 2016).