FGFR3 and Severe achondroplasia - developmental delay - acanthosis nigricans: A study by Bellus at al [46] compared the ligand-independent phosphorylation of FGFR3 mutants implicated in (i) thanatophoric dysplasia type 2 (TD2), (ii) severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN), and (iii) hypochondroplasia (HCH).