Because the branchial arches are important developmental features in a growing embryo, disturbances in their development create lasting and widespread effects.

The syndrome is caused by a mutation in a gene on chromosome 10 that controls the body's production of fibroblast growth factor receptor 2 (FGFR2).

Other facial characteristics that are present in many cases include external strabismus and hypoplastic maxilla (insufficient growth of the midface), which results in relative mandibular prognathism (protruding chin) and gives the effect of the patient having a concave face.

However, the mutation constitutively activates the transmembrane protein via a disulfide bond formed incorrectly due to the loss of cysteine 342.

[citation needed] Surgery is typically used to prevent the closure of sutures of the skull from damaging the brain's development.

Without treatment, Crouzon syndrome can cause hearing and vision loss, exposure keratitis or conjunctivitis, drying of the cornea, hydrocephalus, sleep apnea, and breathing problems.

[medical citation needed] 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.

[citation needed] Once treated for the cranial vault abnormalities, Crouzon patients generally go on to live a normal lifespan.