FGFR3 and acanthosis nigricans: In addition to the FGFR3 family of bone dysplasias, other mutations in this same gene can cause Crouzon syndrome with acanthosis nigricans [97], Muenke syndrome [98], isolated acanthosis nigricans with or without slow linear growth [99–101], and slow linear growth without unequivocal features of a bone dysplasia being present [81].