have a considerable permanent underbite. Causes The current research indicates fibroblast growth factor receptors (FGFR) FGFR2 and FGFR3 as the leading factors in causing the autosomal dominant Crouzon syndrome. These two transmembrane proteins are two of four fibroblast growth factor receptors involved in osteoblast differentiation during embryonic development; mutations amongst these receptors are involved in several genetic disorders. There are 40 known mutations, most of which are caused by a missense mutation. FGFR2 is the most commonly mutated gene, a missense at cysteine 342 in exon 9, which creates a gain-of-function. The FGFR2lllc isoform, created via alternative splicing of exon 3 of the FGFR2 gene, uses exon 9 and is used in mesenchymal stem cells to control ossification. However, the mutation constitutively activates the transmembrane protein via a disulfide bond formed incorrectly due to the loss of cysteine 342. FGFR3 is expressed more in the frontal bones during embryonic development, guiding cranial bone development. A point mutation causes constitutive activation of tyrosine in the activation loop, located in the cytosolic region of the protein, leading to accelerated differentiation of frontal osteoblasts, resulting in premature fusion of frontal cranial bones. Diagnosis Diagnosis of Crouzon syndrome usually can occur at birth by assessing the physical appearance of the infant. Further analysis, including radiographs, magnetic resonance imaging (MRI) scans, genetic testing and CT scans can be used to confirm the diagnosis of Crouzon syndrome. Treatment Surgery is typically used to prevent the closure of sutures of the skull from damaging the brain's development. Without surgery, blindness and intellectual disability are typical outcomes. Without treatment, Crouzon syndrome can cause hearing and vision loss, exposure keratitis or conjunctivitis, drying of the cornea, hydrocephalus, sleep apnea, and breathing problems. To move the orbits forward, surgeons expose the skull and orbits and reshape the bone. To treat the midface deficiency, surgeons can move the lower orbit and midface bones forward. Additionally, surgery can be performed to relieve pressure inside the skull, fix a cleft lip or palate, correct a malformed jaw, straighten crooked teeth, or correct eye problems. People with Crouzon syndrome tend to have multiple sutures involved, most specifically bilateral coronal craniosynostoses, and either open vault surgery or strip craniectomy (if the child is under 6 months) can be performed. In the latter scenario, a helmet is worn for several months following surgery. Once treated for the cranial vault abnormalities, Crouzon patients generally go on to