FGFR3 and Crouzon syndrome: It is present in varying severity and varying frequency in many other FGFR3 disorders, including hypochondroplasia [315, 320–322], thanatophoric dysplasia [86, 87], SADDAN syndrome [93], Crouzon syndrome with acanthosis nigricans [97, 323], and in isolation with little or no skeletal abnormality [99–101].