Crouzon syndrome

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.

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Overview

 This syndrome is named after Octave Crouzon, 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 lead 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 lambdois and coronal sutures), oxycephaly (fusion of coronal and lambdoidal sutures), Kleeblattschaedel ( premature closure of all sutures)

Causes

As stated previously, there is evidence for a genetic basis to this disorder, but there is also no known series of events leading to all the manifestations present. Instead, it is more accurate to view the symptoms arising independently from one another.

As in many syndromes, aberrations in chromosomes seem to be responsible in some cases, and in particular there is support that this disorder may propagate in an autosomal dominant mode. Evidence shown is that males and females are affected equally, and affected offspring tend to have an affected parent. Furthermore, some researchers point to the long arm of chromosome 10 as a possible location for a genetic abnormality.

On the other hand, 20-40% of people with this disorder have no family history of this disorder, meaning that there is little likelihood of a familial inheritance in those cases. Thus, it is believed that a cause may be a fresh mutation, or, alternatively, an environmental disruption of the developing embryo which results in the same physical characteristics as the genetically-derived disorder. In other words, though genetic anomalies may be leading to a disruption of embryogenesis, facts suggest an important role of environmental factors.

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.

Diagnosis

Diagnosis of Crouzon Syndrome usually can occur at birth by assessing the signs and symptoms of the baby. Further analysis, including radiographs, magnetic resonance imaging (MRI) scans, and genetic testing, can be used to confirm the diagnosis.

Incidence

Incidence of Crouzon Syndrome is currently estimated to occur in 1 out of every 25,000 people out of the general population. Naturally, there is a greater frequency in families with a history of the disorder, but that doesn't mean that everyone in the family is affected (as referred to above).

Treatment

Surgery is typically used to prevent the closure of sutures of the skull from damaging the brain's development. Without surgery, blindness and mental retardation are typical outcomes. To treat the cosmetic troubles, a combination of orthodontic and orthognathic surgery can be used to relieve some of the midface deficiency. In addition, many patients wear a custom-fitted helmet (or cranial band) for several months after surgery.

Once treated for the cranial vault symptoms, Crouzon patients generally go on to live a normal lifespan.

Dental significance

For dentists, this disorder is very important to understand since most of the physical abnormalities are presented in the head, and particularly the oral cavity. Common features are a narrow/high-arched palate, posterior bilateral crossbite, hypodontia (missing some teeth), and increased spacing between teeth. Due to maxillary hypoplasia, Crouzon patients generally have a considerable permanent underbite and subsequently cannot chew using their incisors. For this reason, Crouzon patients sometimes eat in an unusual way--eating fried chicken with a fork, for example, or breaking off pieces of a sandwich rather than taking a bite out of it.

See also

• Apert syndrome
• Hearing loss with craniofacial syndromes