Crouzon syndrome is a genetic disorder characterized by the premature fusion of certain skull bones (craniosynostosis). This early fusion prevents the skull from growing normally and affects the shape of the head and face. Crouzon syndrome is seen in about 1 per 60,000 newborns. It is the most common craniosynostosis syndrome.
Many features of Crouzon syndrome result from the premature fusion of the skull bones. Abnormal growth of these bones leads to wide-set, bulging eyes (hypertelorism) and vision problems caused by shallow eye sockets; eyes that do not point in the same direction (strabismus); a beaked nose; short upper lip and an underdeveloped upper jaw. In addition, some with Crouzon syndrome may have dental problems and hearing loss, which is sometimes accompanied by narrow ear canals. Some with Crouzon syndrome have an associated cleft lip and palate. The severity of these signs and symptoms varies among affected people. People with Crouzon syndrome are usually of normal intelligence. No digital abnormalities are associated.
Crouzon syndrome traits include:
- Wide skull
- High forehead
- Wide set eyes
- Protrusion of the eyeballs
- Airway obstruction
- Underdevelopment of the upper jaw
Mutations in the FGFR2 and FGFR3 genes cause Crouzon syndrome. This gene provides instructions for making a protein called fibroblast growth factor receptor 2. Among its multiple functions, this protein signals immature cells to become bone cells during embryonic development. Mutations in the FGFR2 gene probably overstimulate signaling by the FGFR2 protein, which causes the bones of the skull to fuse prematurely. Mutations in FGFR3 gene are associated with Crouzon syndrome with acanthosis nigricans.
This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.