The delayed ossification that characterizes Eiken syndrome suggests that the mutations have gain-of-function (GOF) effects on the activity of the PTH1R expressed in chondrocytes of developing skeletal tissue, as the receptor normally acts in these cells to respond to locally produced PTHrP and hence slow their rate of differentiation and assure the proper shape formation and mineralization of the bone structure17. The gene discussed is PTHLH; the disease is Eiken syndrome.