PDE4A and acrodysostosis: Each PDE4 isoform has a unique N-terminal region that enables it to localize to different intracellular compartments by binding with different scaffolding proteins.1,2 The UCRs are structural and regulatory regions that are unique to PDE4s9 and are responsible for the formation of dimers by long isoforms.10 In the context of acrodysostosis, disease-causing mutations have been localized across UCR1, UCR2 and the catalytic domain.11-13