Elevated levels of CNP and NT-proCNP in achondroplasia are thought to be a natural response of the human body to this overactivation of the MEK/ERK MAPK pathway in chondrocytes, which functionally inhibits the effect of CNP on chondrocytes via NPR-B encoded by NPR2 [69,75]. The gene discussed is NPR2; the disease is achondroplasia.