Crouzon syndrome is a genetic disorder known as a branchial arch syndrome. Specifically, this syndrome affects the first branchial (or pharyngeal) arch, which is the precursor of the maxilla and mandible. Since the branchial arches are important developmental features in a growing embryo, disturbances in their development create lasting and widespread effects.
Symptoms
As a very complicating result of the changes to the developing embryo, the symptoms are very pronounced features, especially in the facial areas. Low-set ears is a typical characteristic, as in all of the disorders which are called branchial arch syndromes. The reason for this abnormality is that ears on a fetus are much lower than those on an adult. During normal development, the ears “travel” upward on the head; however, in Crouzon patients, this pattern of development is disrupted. Ear canal malformations are extremely common, generally resulting in some hearing loss. In particularly severe cases, Ménière’s disease may occur.
The most notable characteristic of Crouzon syndrome is cranial synostosis, as described above, but it usually presents as brachycephaly, which results in the appearance of a short and broad head. Exophthalmos (bulging eyes due to shallow eye sockets after early fusion of surrounding bones), hypertelorism (greater than normal distance between the eyes), and psittichorhina (beak-like nose) are also symptoms. Additionally, a common occurrence is external strabismus, which can be thought of as opposite from the eye position found in Down syndrome. Lastly, hypoplastic maxilla (insufficient growth of the midface) results in relative mandibular prognathism (chin appears to protrude despite normal growth of mandible) and gives the effect of the patient having a concave face.
For reasons that are not entirely clear, most Crouzon patients also have noticeably shorter humerus and femur bones, in proportion to the rest of their bodies, than members of the general population. A small percentage of Crouzon patients also have what is called “Type II” Crouzon syndrome, distinguished by partial syndactyly.
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