Biallelic mutations in the B4GALT7 and B3GALT6 genes, encoding the linker enzymes galactosyltransferase-I (β4GalT7) and -II (β3GalT6), respectively, that catalyze subsequent steps of the GAG tetrasaccharide linker region biosynthesis (Figure 1B), give rise to two subtypes of spondylodysplastic EDS (spEDS), spEDS-B4GALT7 and spEDS-B3GALT6. The gene discussed is B4GALT7; the disease is spondylodysplastic Ehlers-Danlos syndrome.