Klippel-Feil syndrome (Monarch Disease Ontology entry MONDO_0001029) is a congenital, musculoskeletal condition characterized by the fusion of at least two vertebrae of the neck. Common symptoms include a short neck, low hairline at the back of the head, and restricted mobility of the upper spine. This syndrome can cause chronic headaches as well as pain in both the neck and the back.Other features may involve various other body parts or systems. Sometimes, KFS occurs as a feature of another disorder or syndrome, such as Wildervanck syndrome or hemifacial microsomia. In these cases, people have the features of both KFS and the additional disorder. KFS may be caused by mutations in the GDF6 or GDF3 gene and inherited in an autosomal dominant manner; or, it may be caused by mutations in the MEOX1 gene and inherited in an autosomal recessive manner. Treatment is symptomatic and may include medications, surgery, and/or physical therapy. Also known as: Klippel-Feil Sequence.