Fibroblast growth factor receptor 3 (Fgfr3) is a tyrosine kinase receptor expressed in developing bone, cochlea, brain and spinal cord. Achondroplasia, the most common genetic form of dwarfism, is caused by mutations in FGFR3. Here we show that mice homozygous for a targeted disruption of Fgfr3 exhibit skeletal and inner ear defects. Skeletal defects include kyphosis, scoliosis, crooked tails and curvature and overgrowth of long bones and vertebrae. Contrasts between the skeletal phenotype and achondroplasia suggest that activation of FGFR3 causes achondroplasia. Inner ear defects include failure of pillar cell differentiation and tunnel of Corti formation and result in profound deafness. Our results demonstrate that Fgfr3 is essential for normal endochondral ossification and inner ear development.

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FEW WOULD DENY THAT WE LIVE IN A NOISY WORLD. NOISE, whether a result of air traffic, crowded urban streets, personal stereos, or high-powered machinery, rifles, and shotguns, is one of America's most widespread nuisances. Excessive noise disrupts sleep, produces stress, impairs communication, and, in high enough doses, causes significant noise-induced hearing loss (NIHL). Although roughly 25% of all Americans ages 65 and older suffer hearing loss, hearing loss is not part of the natural aging process. Much hearing loss in older Americans is due to preventable, noiseinduced wear and tear on the auditory system.

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