The most common signs of the disorder are restricted mobility of the neck and upper spine and a shortened neck with the appearance of a low hairline at the back of the head.Associated abnormalities may include:
Scoliosis (sideways curvature of the spine)
Spina bifida
Problems with the kidneys and the ribs
Cleft palate
Dental problems (delayed dentition, cavities, missing teeth)
Respiratory problems
Heart defects
Short stature
Duane syndrome
Srbs anomaly
Sprengels deformityThe disorder also may be associated with abnormalities of the head and face, skeleton, sex organs, muscles, brain and spinal cord, arms, legs and fingers. Genetics
Mutations of the GDF6, GDF3 and MEOX1 gene are associated with KFS. The cause of the condition is unknown in individuals with KFS who do not have mutations of these two genes. GDF6 and GDF3 provide the body with instructions for making proteins involved in regulating the growth and maturation of bone and cartilage. GDF6 specifically is involved in the formation of vertebral bones, among others, and establishing boundaries between bones in skeletal development. GDF3 is involved with bone and cartilage growth. Mutations of GDF6, GDF3 and MEOX1 cause a reduced number of functional proteins that are coded by these genes, but it is unclear exactly how a shortage in these proteins leads to incomplete separation of the vertebrae in people with KFS. However, when the GDF6 gene was removed in mice, the result was the fusion of bones.These mutations can be inherited in two ways:

Autosomal dominant inheritance, where one copy of the altered gene in each cell is sufficient to cause the disorder, is especially associated with C2-C3 fusion.
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.