In conclusion, the delayed ossification seen in Eiken syndrome patients with the homozygous R485XPTH1R mutation can now be linked to an increase in basal cAMP signaling activity, as well as a more sustained cAMP signaling response to PTHrP, which appear to result from a deficiency of the mutant receptor in recruiting β-arrestin to endosomes. The gene discussed is PTHLH; the disease is Eiken syndrome.