[Molecular genetic background of developmental bony malformations at the craniocervical junction and cervical spine].

In this review a new interpretation of the origin of bony developmental malformations affecting the craniocervical junction and the cervical spine is presented based on recent advances in the understanding of embryonic development of the spine and its molecular genetic control. Radiographs, CT and MRI scans or CT myelograms of patients with Klippel-Feil syndrome were used for demonstration. Detailed clinical and radiological analysis of these patients was published earlier [David KM, Stevens JM, Thorogood P, Crockard HA. The dysmorphic cervical spine in Klippel-Feil syndrome: interpretations from developmental biology. Neurosurg Focus 1999;6(6):1.]. Homeotic transformation due to mutations or disturbed expression of Hox genes is a possible mechanism responsible for Cl assimilation. Notochordal defects and/or signalling problems, that result in reduced or impaired Pax-1 gene expression, may underlie vertebral fusions. This, together with asymmetrical distribution of paraxial mesoderm cells and a possible lack of communication across the embryonic mid-line, could cause the asymmetrical fusion patterns. The wide and flattened shape of the fused vertebral bodies, their resemblance to the embryonic cartilaginous vertebrae and the process of progressive bony fusion with age suggest that the fusions occur before or, at the latest, during chondrification of vertebrae. The authors suggest that the aforementioned mechanisms are likely to be, at least in part, responsible for the origin of the bony developmental malformations affecting the craniocervical junction and the cervical spine.