PAX1 and Klippel-Feil syndrome 1, autosomal dominant: Skeletal phenotypes have also been observed in Kmt2a+/− mice, including fusion of cervical vertebrae.26 In mouse embryonic fibroblasts, Kmt2a regulates the expression and H3K4 trimethylation of Gdf6 (a gene involved in bone morphogenesis that causes Klippel–Feil Syndrome (KFS)), Pax1 (KFS candidate gene27), and Pax9 (a functionally relevant gene in vertebrate segmentation28).