Gain-of-function FGFR3 mutations lead to dwarfism (ACH, hypochondroplasia, and thanatophoric dysplasia) [5, 30, 31] but also craniofacial suture fusions (craniosynostoses: Muenke syndrome and Crouzon syndrome with acanthosis nigricans) [32, 33]. This evidence concerns the gene FGFR3 and acanthosis nigricans.