Fibroblast growth factor receptor 3 (FGFR3) is a receptor tyrosine kinase that 
plays an important role in long bone development. The G380R mutation in FGFR3 
transmembrane domain is known as the genetic cause for achondroplasia, the most 
common form of human dwarfism. Despite many studies, there is no consensus about 
the exact mechanism underlying the pathology. To gain further understanding into 
the physical basis behind the disorder, here we measure the activation of 
wild-type and mutant FGFR3 in mammalian cells using Western blots, and we 
analyze the activation within the frame of a physical-chemical model describing 
dimerization, ligand binding, and phosphorylation probabilities within the 
dimers. The data analysis presented here suggests that the mutation does not 
increase FGFR3 dimerization, as proposed previously. Instead, FGFR3 activity in 
achondroplasia is increased due to increased probability for phosphorylation of 
the unliganded mutant dimers. This finding has implications for the design of 
targeted molecular treatments for achondroplasia.