Crouzon syndrome is a rare genetic condition affecting primarily the skull and facial bones. It leads to craniosynostosis, involving the coronal sutures, and underdevelopment of the facial bones. Studies have shown that Crouzon syndrome occurs somewhere between 1 in 50,000 and 1 in 100,000 births.
Cause of Crouzon syndrome
Crouzon syndrome has 2 variants. The classic variant is caused by a mutation of the fibroblast growth factor receptor gene FGFR-2, located on chromosome 10. The second variant, notable for the presence of abnormal skin pigmentation called acanthosis nigricans, is the result of a mutation in FGFR-3, located on chromosome 4. In most cases, both of these mutations arise randomly and sporadically. We do not yet fully understand what causes this mutation. However, it does not appear that the mutation occurs as a result of something either parent does or fails to do. In fact, most parents who have a baby with Crouzon syndrome have normal genes.
Children with Crouzon syndrome can pass the gene on to their children, however. These mutations are passed in an autosomal dominant fashion, meaning that only one copy of the gene needs to be passed on for the new baby to have Crouzon syndrome. In practical terms, autosomal dominant inheritance means that there is a 50-50 chance of a parent with Crouzon syndrome having a baby that also has Crouzon syndrome. Anyone with Crouzon syndrome who wishes to have children should consider meeting with a geneticist in order to discuss the risks and make a thoughtful, informed decision.
The skull is comprised of a number of plates of bone, joined together at specialized joints called sutures. These sutures act like expansion joints, allowing the skull to get larger as your child grows and as the developing brain pushes outward. In Crouzon syndrome, two of these sutures (the coronal sutures) fuse prematurely, preventing the forehead from growing forward. Since the brain cannot push the forehead forward as it grows, the brain instead pushes outward and upward in other parts of the skull where these expansion joints are functioning. This leads to a tall forehead that is positionied too far back.
In addition to fused coronal sutures, children with Crouzon syndrome also have underdeveloped bones in the midface, the part of the face lying between the eyes and the mouth. In essence, the bones of the midface do not grow forward as they should. The combined effect of the slowed growth of the forehead and midface is to make the eyes appear large and prominent. In fact, the eyes are normal sized in children with Pfeiffer syndrome. However, they are not as well protected and surrounded by bony structures as they should be, making them appear large.
Additional characteristics of children with Crouzon syndrome include obstructive sleep apnea (related to the underdeveloped midface), conductive hearing loss and a slightly higher incidence of Chiari malformations. Children with Crouzon syndrome typically have normal intellect.
Diagnosis of Crouzon syndrome
Most often, Crouzon syndrome is suspected at birth based on the characteristic appearance of the face and skull. The suspected diagnosis may be confirmed by genetic testing.
Treatment of children with Crouzon syndrome is complex and is aimed at correcting the skull and midface abnormalities and treating obstructive sleep apnea.
- Skull surgery: Although the timing and sequence of surgeries may vary from child to child, most children with Crouzon syndrome will need 2-4 skull operations over a lifetime. The earliest skull surgery is frequently done in the first 18 months of life.
- Midface surgery: The most common surgery for moving the bones of the midface forward in Crouzon syndrome is called a LeFort III operation. This surgery is typically not done before your child is 6-8 years of age. The primary indications for performing a LeFort III operation include severe obstructive sleep apnea which cannot be improved without surgery or significant patient concerns about appearance. During this operation, the bones of the midface are cut across the top of the nose, along the floor of the orbits and across the cheekbones. Most of these cuts may be made through the same incision used for your child's other skull surgeries. An additional incision may be placed on the inside of the mouth. No scars are placed on your child's face. After making these cuts, the bones are either moved immediately into their final position and secured in place with plates and screws or moved gradually by a process called rigid external distraction. Which of these techniques is used depends on the age of your child at the time of surgery and the distance that the bones must be moved.
- Obstructive sleep apnea: Children with Crouzon syndrome frequently have obstructive sleep apnea due to the underdevelopment of the midface. As a result, your child should be monitored for sleep apnea by your craniofacial team. In mild cases of sleep apnea, medications may be sufficient to improve breathing. If more significant obstruction occurs, tonsillectomy or continuous positive airway pressure (CPAP) masks may help alleviate symptoms. Rarely, a tracheostomy may be required in infants with Crouzon syndrome in order to ensure adequate breathing. Midface surgery, such as a LeFort III operation, may be needed as your child gets older in order to fully treat obstructive sleep apnea or allow for eventual removal of a tracheostomy place in infancy. Ultimately, the goal in all of these interventions is to ensure a good airway so that your child can get enough oxygen to help her develop to her fullest potential.