- Novel mutations in DLL3, a somitogenesis gene encoding a ligand for the Notch signalling pathway, cause a consistent pattern of abnormal vertebral segmentation in spondylocostal dysostosis. Turnpenny, P.D., Whittock, N., Duncan, J., Dunwoodie, S., Kusumi, K., Ellard, S. J. Med. Genet. (2003)