FGFR3 and thanatophoric dysplasia: The same analysis performed in those with hypochondroplasia demonstrated that CXM levels were not statistically different than controls, whereas individuals with thanatophoric dysplasia showed very low levels of CXM demonstrating a correlation between the degree of FGFR3 overactivity resulting in varying clinical phenotypes of FGFR3-related skeletal disorders and biomarker concentration [23].