GDF6 and Klippel-Feil syndrome 1, autosomal dominant: While mutations in the TGF-β superfamily ligands GDF6 and GDF3 have been shown to cause KFS, KFS can be genetically heterogeneous (Tassabehji et al., 2008; Asai-Coakwell et al., 2009; Ye et al., 2010).