Autosomal recessive inheritance, where both copies of a gene contain mutations, is especially associated with C5-C6 fusion. Another autosomal dominant form (mapped on locus 8q22.2), known as KFS with laryngeal malformation, has been identified. It is also known as segmentation syndrome 1. Diagnosis
The heterogeneity of KFS has made it difficult to outline the diagnosis as well as the prognosis for this disease. Classification
In 1912, Maurice Klippel and Andre Feil independently provided the first descriptions of KFS. They described patients who had a short, webbed neck; decreased range of motion (ROM) in the cervical spine; and a low hairline. Feil subsequently classified the syndrome into 3 categories:
Type I—Fusion of C2 and C3 with occipitalization of the atlas. In 1953, further complications were later reported by McRae; flexion and extension is concentrated within the C1 and C2 vertebrae. As with aging, the odontoid process can become hypermobile, narrowing the space where the spinal cord and brain stem travel (spinal stenosis). Type II—Long fusion below C2 with an abnormal occipital-cervical junction. Similar to the C2-C3 fusion of McRae and could be viewed as a more elaborate variation. Flexion, extension, and rotation are all concentrated in the area of an abnormal odontoid process or poorly developed ring of C1 which cannot withstand the effects of aging. Type III—A single open interspace between two fused segments. Cervical spine motion is concentrated at single open articulation. This hypermobility may lead to instability or degenerative osteoarthritis.
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