FGFR2 and Apert syndrome: Over 98% of Apert syndrome cases are attributed to two amino acid substitutions, Ser252Trp (S252W) and Pro253Arg (P253R), which are located in the linker region between the second and third extracellular Ig domains of FGFR2 (Park et al., 1995; Wilkie et al., 1995).