Description, Causes and Risk Factors:
Alternative Name: Type III acrocephalosyndactyly, Chotzen syndrome.
Saethre-Chotzen syndrome (SCS) belongs to a group of rare genetic disorders known as acrocephalosyndactyly disorders. All are characterized by craniosynostosis (premature ossification of the skull and obliteration of the sutures. The particular sutures involved determine the resultant shape of the malformed head), the premature fusion of the cranial sutures, causing acrocephaly (a congenital abnormality of the skull; the top of the skull assumes a cone shape), and syndactyly (birth defect in which there is partial or total webbing connecting two or more fingers or toes).
SCS is one of the most common syndromic forms of craniosynostosis in humans. Clinical features of SCS include acrocephalosyndactyly most commonly affecting the coronal suture, dysmorphic facial features (e.g., facial asymmetry, hypertelorism and maxillary hypoplasia), low frontal hairline, brachydactyly (abnormal shortness of finger) and cutaneous syndactyly. Additional physical findings can include tear duct stenosis, vertebral fusion, and mild short stature.
SCS is inherited as an autosomal dominant trait with a high penetrance and variable expression, and has an estimated birth incidence of 1/25,000 to 1/50,000.
A person with SCS has a 50% chance for each pregnancy of passing this mutation on to the child. Although it is a genetic condition, the parents of most children born with SCS do not have SCS themselves. The mutation can occur in any child at the time of conception.
The locus for SCS was mapped to chromosome 7p21-p22, and mutations in the TWIST1 gene encoding a basic helix-loop-helix (bHLH) transcription factor, were identified. The TWIST gene product is a transcription factor containing a basic helix-loop-helix (bHLH) domain, required in head mesenchyme for cranial neural tube morphogenesis in mice. The types of TWIST1 mutations found in individuals with SCS (insertions and deletions, nonsense mutations, and missense mutations in the DNA binding domain) suggest that these mutations would lead to the production of truncated or non-functional TWIST1 protein. Microdeletions that encompass the entire TWIST1 gene have also been identified in SCS patients. These data indicate that the predominant cause of SCS is haploinsufficiency for the TWIST1 gene.
Although most patients with the SCS have mutations in the TWIST gene, some patients with an overlapping phenotype have a mutation in the FGFR3 gene and at least one individual has been described with a mutation in the FGFR2 gene.
About one third of children with SCS have some webbed fingers or toes.
Several other less-common differences can be present, including cleft palateand short stature.
Most children with SCS have differences in the shape of their face and head.The most common difference is a lopsided or a tall flat forehead. Other more minor symptoms, like droopy eyelids or a crooked nose, are often not noticed by families.
To diagnose this condition, your doctor will examine your child's skull carefully. The shape will help the doctor tell whether any sutures have fused.Your child's features, like their eyelids, will help the doctor determine whether they have SCS or another condition.Your doctor may also do genetic tests that show whether your child has a mutation that causes SCS.
A CT scan is an X-ray procedure that takes a computer-enhanced cross-sectional view of the body.
Computed tomography (CT) imaging can give the doctor more information.
Very often, the physical characteristics are so mild that no surgical treatment is necessary. Facial appearance tends to improve as the child grows; however, the following may by necessary:
Surgery to correct the webbing of the fingers.
Reconstructive surgery to eyelids and nose.
Surgery to correct the fusion of the cranial structures.
The craniosynostosis affects the coronal sutures, usually both, producing a short wide head (brachycephaly), occasionally only one side is affected and this produces an asymmetrical head (plagiocephaly). These abnormal-shaped heads can be corrected, but there are two different reasons for doing this.
Firstly, the skull may not grow as quickly as the brain and lead to raised pressure around the brain. If this happens then an operation is usually advised to make the skull bigger, to allow the pressure around the brain to be normal, and so the brain can grow.
Secondly, the appearance may need to be improved surgically, especially in the unicoronal cases. There are times when operative intervention is advised for both of these reasons. The droopy eyelids (or ptosis), usually present no problems but can on occasion be so severe as to impair upward gaze. This may require surgical correction which is a relatively minor plastic surgery procedure. A squint may also be associated with the condition requiring ophthalmological care. The joining of the bones (vertebrae) in the neck, if it occurs, usually only affects the two adjacent vertebrae. These fusions occur after birth during childhood. Currently, there are no known adverse effects directly resulting from these but care must be taken during anaesthetics and radiographs may be taken prior to surgery.
The short fingers and the joining of the fingers (syndactyly) rarely cause any problems. The joining, if it occurs, often only affects the base of the fingers and is unlikely to affect function of the hand. There are no reports of anyone with the condition requiring surgery for their hands.
The growth of the bones of the hands is often delayed during childhood but again there are no clinical implications resulting from this. The feet may have broad toes, as occasionally the bones at the ends of the toes attempt to duplicate themselves. The big toe is most commonly affected and this does not present any problems clinically. The children walk at the normal time and should have no difficulties with footwear. Other joints have on occasion been reported to be affected but these must be extremely rare and may just reflect uncertainty regarding the diagnosis.
The ears too have been reported as having a higher incidence of minor anomalies but the significance of these remain unclear.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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