Klippel-Feil sequence Health Article

Definition

Individuals with Klippel-Feil sequence (KFS) were originally described as having a classic triad of webbed neck (very short neck), low hairline, and decreased flexibility of the neck. More commonly, abnormal joining or fusion of two or more vertebrae (bones) of the cervical spine (neck bones) characterizes Klippel-Feil sequence.

Description

Klippel-Feil sequence is extensive fusion of multiple cervical vertebrae (the uppermost bones of the spine). There may be complete fusion or multiple irregular bony segments in the bones of the upper back (cervical and often upper thoracic spine). Premature and extensive arthritis and osseous (bony) spurring affecting the joints of the spine (facet joints) are common in individuals with Klippel-Feil sequence.

There are three classifications of Klippel-Feil sequence.

• Group 1 exhibits fusion of the lower skull (head) and the first bone of the spine (the first cervical vertebrae (C1)). The second and third spinal bones (cervical vertebrae C2 and C3) are also usually fused together in Group 1. The normal cervical spine has seven bones or vertebrae. Normally half of the ability of humans to bend their heads forward (flexion) and backwards (extension) occurs in the joints between the base of the skull and the uppermost spinal bone. The other half of the motions of flexion and extension occur in the rest of the upper spine. Therefore, the danger is due to the excessive motion of the neck between the joints that are fused.
• Group 2 has fusion of bones (vertebrae) below the second cervical bone (C2). Group 2 also has an abnormal skull and upper spinal bone connection.
• Group 3 has an open space between two fused segments of spinal bones.

Genetic profile

Although this is usually a sporadic occurrence, an abnormal gene responsible for Klippel-Feil sequence has been found on the q (long) arm of chromosome 8. The human cell contains 46 chromosomes arranged in 23 pairs. Most of the genes in the two chromosomes of each pair are identical or almost identical with each other. However, with KFS individuals, there appears to be a reversal or inversion on part of chromosome 8.