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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.
This syndrome is named after Octave Crouzon,[1][2] a French physician who first described this disorder. He noted the affected patients were a mother and her daughter, implying a genetic basis. First called “craniofacial dysostosis”, the disorder was characterized by a number of clinical features; as of 2007, the disorder has no known single, initiating defect to account for all of its characteristics.
Breaking down the name, “craniofacial” refers to the skull and face, and “dysostosis” refers to synostosis (a union between adjacent bones or parts of a single bone).
Now known as Crouzon Syndrome, the disease can be described by the rudimentary meanings of its former name. What occurs in the disease is that an infant’s skull and facial bones, while in development, fuse early or are unable to expand. Thus, normal bone growth cannot occur. Fusion of different sutures leads to different patterns of growth of the skull. Examples include: trigonocephaly (fusion of the metopic suture), brachycephaly (fusion of the coronal suture), dolichocephaly (fusion of the sagittal suture), plagiocephaly (unilateral premature closure of lambdoid and coronal sutures), oxycephaly (fusion of coronal and lambdoidal sutures), Kleeblattschaedel ( premature closure of all sutures).
Associations with FGFR2[3] and FGFR3[4] have been identified.
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.
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