FGFR3 and achondroplasia: However, in a study involving mice in which one allele of the Fgfr3 gene was replaced with a constitutively active form, as occurs in achondroplasia, it was found that treatment with the CNP analog increased the growth rate of cultured tibia only partially, from ~40% to~70% of wild type (Lorget et al., 2012).