The cause of craniosynostosis largely depends on whether it is syndromic (exists with other birth defects) or nonsyndromic (there are no other defects).
Sometimes, the cause is not known.
Causes of nonsyndromic craniosynostosis
The cause of nonsyndromic craniosynostosis is unknown. However, a number of theories have been suggested.
One theory is that nonsyndromic craniosynostosis may be caused by the baby adopting an unusual position in the womb. For example, if the baby's head is pushed down by their mother's ribcage, this will place pressure on their skull. This extra pressure may push the plates of bone together, causing the sutures in the skull to fuse too soon.
Other theories suggest that an unidentified defect in the cells that make up the sutures causes them to fuse prematurely, or that a signal from the brain itself results in the abnormal fusion.
Most cases of nonsyndromic craniosynostosis do not appear connected to anything that a mother does during pregnancy. Women who took a medication called valproic acid (sodium valproate), used to treat epilepsy, during pregnancy were thought to be at increased risk of having a baby with craniosynostosis, although recent studies have failed to confirm this.
Causes of syndromic craniosynostosis
Although it is rarer, more is known about the causes of syndromic craniosynostosis.
There are many syndromes that can cause this form of craniosynostosis, including:
- Apert syndrome
- Crouzon syndrome
- Pfeiffer syndrome
- Saethre-Chotzen syndrome
Most cases of syndromic craniosynostosis are caused by one of four genetic mutations. A genetic mutation occurs when instructions carried in certain genes (a unit of genetic material) become scrambled. This means some of the body's processes do not work in the normal way.
Examples of mutated genes in craniosynostosis are:
- FGFR1, FGFR2 and FGFR3 (three related genes)
- TWIST gene
The FGFR group of genes seem to make a protein called fibroblast growth factor receptor work less effectively. As this protein is involved in regulating cell growth, particularly the growth of bones, it is thought the FGFR mutation disrupts the development of the skull.
The mutated TWIST gene seems to totally block the effects of fibroblast growth factor receptors. There are often a wide range of birth defects associated with this gene.