What are the types of Klippel-Feil Syndrome?
Klippel-Feil Syndrome (KFS) can be divided into several classes or types with a range of health issues, but all forms share the main feature which is fusion of at least two of the seven neck bones in the spine (cervical vertebral fusion) that happens before birth. Specific health problems present in KFS often are different from one individual to another and all of the symptoms may not occur in one person.
In the original classification of KFS, Maurice Klippel and Andre Feil organized groups of individuals based on the degree of cervical fusion:
- Type I: Extensive fusion of vertebrae of the neck (cervical vertebrae) and the upper back (upper thoracic vertebrae)
- Type II: Fusion of one or two vertebrae of the neck (cervical vertebrae) or upper back (thoracic vertebrae)
- Type III: Fusion of neck vertebrae as well as vertebrae of the upper or lower back (lower thoracic or lumbar vertebrae)
In the most recent classification system by Clarke, individuals with KFS are divided into groups based on the way the condition runs in the family, the level at which the cervical vertebrae are fused, and health issues seen in addition of the fused cervical vertebrae:
- Class 1: Highest level of fusion at the C1-2 cervical vertebrae, a very short neck, and autosomal recessive inheritance
- Class 2: Highest level of fusion at the C2-3 cervical vertebrae and an autosomal dominant pattern of inheritance
- Class 3: Highest level of fusion between any of the cervical vertebrae (except C1-2), limited to no other medical issues related to KFS, and recessive inheritance of KFS through the family.
- Class 4: Any fusion of any cervical vertebrae, hearing impairment present at birth, and Duane syndrome [unusual eye (ocular) movements including limited or absent horizontal eye movements, retraction or "moving back" of the eyeball into the eye cavity (orbit) upon attempting to look inward, and, in some cases, crossed eyes]. Mainly affects females. Class 4 is also called Wildervanck syndrome.
Klippel-Feil Syndrome, NORD, https://rarediseases.org/rare-diseases/klippel-feil-syndrome/
"Wildervanck syndrome", NORD, https://rarediseases.org/rare-diseases/wildervanck-syndrome/