PURPOSE: There are a number of craniosynostosis syndromes with hearing 
loss-including Muenke, Apert, Pfeiffer, Crouzon, Beare-Stevenson, Crouzon with 
acanthosis nigricans, and Jackson-Weiss syndromes-that result from mutations in 
the fibroblast growth factor receptor (FGFR) genes. Studies of FGFRs and their 
ligands, fibroblast growth factors (FGFs), have revealed clues to the precise 
contribution of aberrant FGFR signaling to inner ear morphogenesis and the 
hearing loss encountered in craniosynostoses. The purpose of this article is to 
review basic studies of FGFRs with emphasis on their function and expression in 
the inner ear and surrounding structures.
METHOD: A Medline search was performed to find basic science articles regarding 
FGFR, their ligands, and their expression and relevant mouse models. Additional 
items searched included clinical descriptions and studies of individuals with 
FGFR-related craniosynostosis syndromes.
RESULTS: The FGF signaling pathway is essential for the morphogensis and proper 
function of the inner ear and auditory sensory epithelium.
CONCLUSION: The variable auditory phenotypes seen in individuals with Muenke 
syndrome may have a genetic basis, likely due to multiple interacting factors in 
the genetic environment or modifying factors. Further analysis and studies of 
mouse models of Muenke syndrome, in particular, may provide clues to the 
specific effects of the defining mutation in FGFR3 in the inner ear not only at 
birth but also into adulthood. In particular, investigations into these models 
may give insight into the variable expression and incomplete penetrance of this 
phenotype.