Acanthosis nigricans (AN) has been reported in association with severe skeletal dysplasias due to activating mutations in FGFR3, including thanatophoric dysplasia, severe achondroplasia (ACH) with developmental delay and AN (SADDAN syndrome), and Crouzon syndrome with AN.
Fibroblast growth factor receptors 3 (FGFR3) with K644M/E substitutions are associated to the severe skeletal dysplasias: severe achondroplasia with developmental delay and achanthosis nigricans(SADDAN) and thanatophoric dysplasia(TDII).