In achondroplasia, the normal reciprocal antagonism10 between FGFR3 pathway activity (inhibitory to endochondral bone growth) and CNP signalling (stimulating bone growth) is overridden by a gain of function mutation in FGR311, reducing intracellular CNP activity, and is associated with modest elevations in concentrations of CNP products in plasma6. The gene discussed is CNP; the disease is achondroplasia.