XYLT1 and spondylo-ocular syndrome: The different clinical manifestations between Desbuquois skeletal dysplasia type 2 and spondyloocular syndrome may indicate that XYLT1 and XYLT2 do not compensate for each other, and that the serine residue(s) of the respective core protein as a substrate for each XYLT and spatiotemporal expression may be distinct between XYLT1 and XYLT2.